Don't try to play one game with six players. It doesn't work, for the exact spotlight-time problems you're concerned about. Five is doable, but be prepared for it to be an incomplete introduction to the game.
Microscope is a wonderful game, but it does not scale up past five players very well at all. I have a hard time introducing the game to new people even with only five players — new players means slower turns, and more people means longer between turns — and it usually only results in one Focus being completed in an evening, and sometimes not even that. Partly this is because I take the game's advice to make Scenes early and often (I find that getting fewer history turns but more Scenes makes for a better introduction to the game than more turns and fewer Scenes).
For your group especially, jumping straight into a Scene during the very first player's turn (you, probably, if you're following the teaching-the-game advice in the back) is the best way to get right into the roleplaying that they're expecting to be learning about tonight.
I've found that the ideal for new groups is 3–4 players. Five is doable, but expect to get much less history made than you'd expect (or more history, but not much roleplaying of characters) unless you have in excess of three hours.
Split a large group into separate games
If you find yourself with a group that's six or larger, divide into smaller groups. Have the group you're in be the "demo" group, and have the other group(s) players watch the first group play through the setup and the first history creation by the first Lens. Then pause the first group and help the other group(s) get started for a few minutes. Now that everyone has seen how the game starts, everyone is able to start a game and you don't need to facilitate as much.
Be ready to leave your game for a few minutes when other games get to playing a Scene to help facilitate that for the first time, too. Since often a game can roll just fine without the facilitator once the idea of making history is understood, you'll have a bit of time to drop out and return without disturbing the flow of your game or them missing your facilitation at all, or much.
Sometimes the only way to win is not to play.
Our hobby, unfortunately, has some necessary prerequisites. The primary one being "willingness to engage in the hobby." Your "player", by not involving herself with rules nor involving herself in the world nor involving herself in the mechanics nor involving herself with the rest of the group... fails this requirement. This game is not suitable for her, nor is much of the hobby, save without specific design for people with similar difficulties.
Microscope is not a rules heavy game, but it does have rules that must be abided by. It does not provide for vetoes once the palette has been established, that being contrary to the intention of everyone laying down their own facts. Given that it's entirely powered by creativity and imagination, I imagine it's rather too complex for your player's intended "menu of options."
The entire point of the game is to decide the course of history. Passivity cannot work. There are no observers, there are only creators. And the only interesting history is one where the players have conflicting motivations.
Best Answer
A period can be any amount of time that makes sense in the context of your history
When the rules say you don’t specify the length of a Period, that doesn’t mean it has no beginning and no end - only that you don’t define it by those things in terms of time. The important thing about a Period is its description; from page 22:
In the example, “the Gods curse the world with endless winter” is a great “grand summary” of what happens in this Period. It also shows what’s different from the Periods around it: specifically, before this Period there was no endless winter.
That doesn’t mean this Period lasts forever, though the effects of what happens during it might. Later Periods might refer to major developments while the endless winter goes on, or perhaps a hero somehow ends the winter after it has lasted for generations. This Period is thus the time when the endless winter began, and the people of the world had to adapt to it.
A similar example might be “the gods sunder the spirit world from the world of mortals”. There can be many Periods after this, even though the spirit world may forever remain separated from the mortal realm. (Though they could also be reunited, if a later Period is defined that way.)