Firstly, you should talk to all your players about the issue outside of a session. You can get some personal impressions first with one-on-one conversations, but ultimately the entire group should sit down to discuss the problems. Make sure the discussion is democratic in nature, though. JohnP points this out in a related question: "The group setting can be dangerous, as it can turn into people digging up old grievances or ganging up on a particular person."
During the discussion you should ensure that everyone is on the same page about how they want the game to be played. The same page tool is a useful set of questions that will drive the discussion in the right direction. Just make sure everyone is fully involved in the discussion and are voicing their opinions clearly (no passive-aggressive bs). If your players are open to compromises a consensus should be reached.
Secondly, make sure your friend is not suffering from My Guy syndrome. If the description matches (and it sounds like it does), show her the link privately and let her think about it. It should help her be more aware of her role as a player and hopefully remedy some of the issues.
You also mentioned your player gets upset as a result of your decisions. This related question contains a lot of suggestions for how to handle players that take things personally, ranging from studying your own approach to kicking out the problematic player.
In the end, though, you are the GM. You are the writer of half of the story, the referee on all mechanics, and the leader in the quest for fun. The way you drive your campaign is part of your style and your players should respect it. They need to be aware that your goal is always to increase the enjoyment they collectively get out of your game. A certain level of trust and respect is absolutely necessary. If this is impossible to obtain in your group, then the group as it is cannot function. Kicking out players or stepping down as GM would be the next steps to try.
Because the GM is so special, though, new players often fail to grasp just how complex the GM role can be, and can at times see him as an enemy and spoilsport. A neat "trick" you can use to show your players what being a GM is really about (that also gives you some rest from the responsibility of being a GM) is to have another person in the group be the GM for a few sessions. It doesn't have to (and most often shouldn't) be the same campaign you're running. Instead, it can be a few sessions of an off-shoot campaign. It's fun for the players because they get the chance to try out new (and often times silly) character builds, and the new GM will discover what it feels to have all this responsibility. Once everyone has GM-ed a couple of sessions, you will all have an idea of who's best at it and will work towards keeping that person as GM in the future. There's a chance it might not be you, but in the end it should result in a better experience overall.
Keep in mind that not everyone is fit for GM-ing, or willing to try at all. Don't force players to GM, and if they decide to try, encourage them to design very short adventures (no more than three sessions). They can always expand on them later if they like it, or end them early if they don't. The player that questions your decisions often probably thinks they can do a better job, so they're likely to accept your offer to prove themselves.
In FR the dragons were created by the primordials. Does this mean many/most/all dragon gods are also primordials, as aspects/fragments of Io?
The Dragon Gods are presented as actual gods rather than primordials (DMG p. 10, PHB p. 296, & SCAG p. 113).
Can a primordial also be (or somehow become) a god?
I'm unaware of this occurring, but I wouldn't rule it out:
- Asgorath/Io is both, but (as creator of the universe) doesn't count.
- Tharizdun is close, but is not a Primordial.
- Kossuth is also close, but he's "not a true god but actually an
elemental primordial".
Do primordials need, desire or benefit from followers?
Not normally, but Kossuth is an example of a primordial that benefits from extensive worship.
Do surviving primordials have significant religions associated with them, either in Abeir or in Toril?
On Toril the five Elemental Lords have followings, while The Seven Lost Gods were once worshiped. I believe Abeir would have more significant Primodial worship, but that setting was never detailed.
Do primordials grant spells in the same way as gods?
Not normally, but again: Kossuth is an example of a primordial that both grants spells and has extensive followings.
Can they be warlock patrons?
I don't see anything preventing this. A few homebrewed examples of this can be found here and here.
Is there any obvious difference in the portfolios of primordials versus gods? I would have assumed that since they predate mortals they tend to represent more fundamental forces (like the elements) rather than human concepts like law, love, luck, agriculture.
That might be one way to view it, but 4e's creation myth (Worlds and Monsters p.56, cited below) has the Gods being created at the same time as the Primordials. Another way to view it might be that the Primordials are composed of elemental "physical-matter" while the Gods (and Astral Sea) are more composed of thought (mental-matter).
In short, what is the difference between a god and a primordial? Are they fundamentally the same (just different lineages) or are there fundamental differences?
They are consistently presented as having fundamental differences. From 4e's Worlds and Monsters (p.56): "The gods, beings of divine power, appeared in the Astral Sea, while in the Elemental Chaos arose the primordials, incarnations of tremendous elemental might"... "composed partially of creation-stuff".
I also found this fantastically detailed post on Candlekeep...
That still seems like as good a guide as any.
Best Answer
In my experience, regardless of what RPG system you use (at least almost, I'm sure there are exceptions), you're going to run into situations where the game's reality is fundamentally different from ours in some way.
One of the great things about RPGs is they can challenge our worldviews and put us in situations we might never get to experience otherwise, allowing us to explore worlds full of "what ifs." If your player isn't interested in exploring those kinds of situations, then maybe RPGs aren't their kind of game, and that's OK!
There could be many reasons why your player is unable or unwilling to suspend their disbelief and explore this kind of alternate reality, and the only way to understand where they're coming from is to have an open and honest discussion with your player.
You mention polytheism as the primary concern, here, but there are other things to consider, too. There may be additional conflict regarding topics like the undead, resurrection, demons, devils, or even the idea of magic and casting spells (there is/was much discussion about this sort of thing with the Harry Potter series, for example). These are all essential topics to bring up in conversation with this player and see how they feel about these ideas before they're potentially thrust into a situation they're uncomfortable with.
I haven't encountered this explicit situation where a religious player is unwilling to adapt, but I've experienced plenty of other scenarios where people were resistant to the unknown, the unfamiliar, or something they believed was "wrong" for various reasons. What's worked for me in the past is to try to understand where they're coming from while looking for ways to draw connections between their viewpoints and the scenario at hand. You should definitely be willing to be flexible, but there's only so much flexibility you can afford before you start making the kinds of large changes you've mentioned you want to avoid.
Some immediate examples of things to draw on include classic fantasy series like C.S. Lewis's The Chronicles of Narnia or J.R.R. Tolkien's The Lord of the Rings. Both of those authors had strong religious beliefs yet were able to translate them to fantasy settings that in turn played a part in inspiring D&D. Look for common ground in your conversation with this player. Find what they do or don't like about fantasy, and see where you can meet in the middle. Then have a talk with all the players together and set expectations. This kind of conversation has worked for me in the past - setting expectations early and having one-on-one discussions about issues of concern goes a long way. I have pre-empted issues many times - not just in RPGs - by speaking with an individual or a group beforehand about expectations. When our expectations were in conflict, sometimes we were able to discuss and reach a compromise or a better understanding of the situation. Other times there was not much willingness to compromise, and that’s when you have to make the unfortunate call of whether it’s worth it to try to push through, or just cut the individual loose. The important thing is not to single this player out and say things like "how could you possibly think that" and "don't you know it's just pretend," etc. Ridicule isn't a great way to discuss things in general, but it's a particularly poor choice when someone is already having a strong emotional reaction to the topic at hand.
The long and short of it is, there's not a great way to "convince" your player to play D&D, nor would I particularly recommend pushing too hard if this player decides it isn't for them. However, there's also not a great way to sculpt D&D to strictly conform to their ideals without potentially making some big changes to the setting or perhaps even certain game mechanics. It's all about perspective, and hopefully your player can come around to the idea that we play fantasy characters in a fantasy world that is fundamentally different than ours.
If not, then the answer may be that you just don't play D&D with them.
The common wisdom is "no gaming is better than bad gaming," and I've seen this especially hold true for new players in RPGs. If it's a negative experience for someone, regardless of reason, that person is unlikely to want to try again. Remember to consider the experience for everyone at the table.