I have a lot of experience with players that act that way. I've had a player like that, at one time or another, so often that it sounds like you're describing my old games.

The one thing I will mention is that this is obviously something out of character related. She is frustrated, annoyed, angry, depressed, or some other emotion about something. And she's taking it out on the game. Since you only have four people and one of them has to be a DM, it's a hard situation to deal with.

This gets a bit into interpersonal skills and might not really be the best place to talk about this, but since you seem to be having a problem, here's what I can offer.

She doesn't want to play the game

It's very obvious from just the first two instances you posted that the player genuinely doesn't want to play the game. Playing a game is about getting into character and rolling with the punches. No plan will be perfect, your character won't know everything, and you're going to get into situations that you are not prepared for. Dealing with all of that is what makes the game fun. It's clear that she just wants to auto-pilot and coast through every scene. And you throwing wrenches into the plans is causing her to get aggravated. This is because she doesn't really want to 'play'.

She doesn't know what it means to roleplay

Maybe she's new to role playing completely, which is an option. If that's the case, she's having a large disconnect with what she 'thinks' she knows and what she actually knows. There is something to be said for a character actually having knowledge of a situation. But then, there's the world-building aspect. There are certain things that the DM will decide that the player has no control over. In fact, this should usually happen. And a player can discuss with a DM about the things they do and don't know or how they should and shouldn't act. But it should never be a case of 'I would never do X' when it's clearly against her character.

She doesn't want to play your particular quest line

I don't know your party dynamic, but it seems like she's poking holes in your game without reason. There is ample place for a party to get involved and have fun doing something in the scenario you've set you. However, she's actively making a character-breaking decision to not go along with the party. The group around the table should NEVER have to discuss for hours about going one place or another. This is a side affect of trying to pull a stubborn mule. The mule doesn't want to go and is going to make everyone else miserable as they try to drag it somewhere it doesn't want to go. And that's what she's being, a stubborn mule. It seems she doesn't want to play your particular side quest, for whatever reason. Maybe she liked the other DM better? Maybe she has something against you? I really can't say, as I don't know your friends.

The Solution

Since you have such a small group and you guys seem to be in the middle of a campaign that someone else is technically running, your options are limited. I would tell you to just let her know that her actions are pretty destructive to everyone's fun and inform her that she's not welcome if she's going to be a petulant child (use better words then that). But, you'd be down a player in the middle of a campaign, and that could hurt your friendship and game.

My suggestion would be to sit down with her, one on one, and talk to her about what's bugging her about the game. She might go over the little details and reiterate what she's said in game, but try to push past that and get to the root of the problem. See what she's really upset about. Maybe home troubles? Maybe someone at the game is frustrating her? Try to figure out possible ways you can tailor the game more to what she's feeling. Maybe she's sick of playing the previous type of character or it's not what she was hoping for. That happens. Try to work with her to either play something different or focus the game more on what she could like doing (keeping in mind the other players interests as well).

One thing I wouldn't suggest is an intervention. Those end badly, simply because the player will feel everyone is ganging up on her and alienating her from the group. Try to keep it one on one with her and let her know that you're just trying to help her have a good time.

My suggestions, coming from the other side of the fence where I (and some of the other players) feel that the DM plays a little too fast and loose with the rules, and makes changes to things that we think ought to be "canon" for the well-known world we are playing in:

1) Be willing to consider that the player may be right. Allow him to make a brief argument referencing the rules. Then make a ruling. Make a mental note of how often you rule against the player versus how often you change your mind and agree with him, and try (later, outside the session) to assess whether you're being particularly harsh and/or truly weakening one character's abilities relative to the others'.

2) Be firm if you still disagree with him. If he still disagrees with your ruling, tell him, "I need to ask you to go with the DM ruling for the moment and we can discuss it more later outside of game time, to figure out how we'll play this type of situation in the future."

2a) Try to offer the player another way to reach his objective. Say something like, "Look, the rules say that you give away your position if you attack from hiding. If you then, in full view of the enemy, duck behind the same tree, they are going to know where you are, even if you are so well hidden that they can't perceive you. Thus you do not get the advantages of being hidden in that case. Now if on your next turn you stealthily move to the next tree and hide there without being noticed, and then attack, that would be unexpected and give advantage."

3) Ask players not to use the Monster Manual at the table, and to avoid using metagame knowledge about monsters. That said, try not to mess with well-known monsters in a canonical setting without a really good story justification. If you're playing in a canonical setting, Mummies are going to be something that most adventurers will know the legends of, and the way that Mummies are described in this universe really does preclude a "good-aligned Mummy". If there's going to be a good-aligned Mummy, there should be a good story to go with that, to say how that happened contrary to the usual Mummy creation process, that the PCs have at least been given hints about. Otherwise, yeah, it's pretty appropriate for a PC to automatically kill any Mummy he comes across on sight. They will know the stories....

Note that the 5e MM does say (page 7 if need a reference for your rules lawyer):

The alignment specified in a monster's stat block is the default. Feel free to depart from it and change a monster's alignment to suit the needs of your campaign. If you want a good-aligned green dragon or an evil storm giant, there's nothing stopping you".

However, unless there is a good story behind the anomalous alignment, and your PCs have access to clues about that story, I think it would usually be better (and annoy your players less) if you either make up a new monster that isn't in the MM, or be clear that you are playing in a non-canonical setting and using monsters that don't match the descriptions in the MM. Even in a canonical setting, you can play variations on less-legendary monsters, but be clear (out of character) with your players that this is what you are doing. In all cases, allow the players relevant checks to recall some in-game, in-setting lore about the monster you are actually playing.

For example instead of just putting in a good-aligned Mummy you could say, "You see a medium-sized humanoid, wrapped in bandages. Make a religion check". Tell everyone with a low score that they think it's a Mummy. Tell whoever got the highest check, "Because of [some detail that they can perceive] you think this might not be a true Mummy but rather a Pseudo-Mummy. Pseudo-Mummies are created by a different process than True Mummies and in some cases can maintain their pre-death alignment." If you want, you can go into the process more, or you can just say that the character doesn't know any more than that. Now you have a good-aligned Mummy that your player shouldn't complain about.

4) Consider having a talk with the players about what game everyone wants to play. You have a conflict in play style with the "rules lawyer" player. Do the others also want to play "his" game, or do they prefer your approach? Can whoever is in the minority live with adjusting their expectations to what the group as a whole prefers? Can there be some compromise?