Thoughts about Simone, I have them!
When we first meet her, she is a friendly, kind person with awesome boundaries, who sees her relationship with Chidi as a terrific "optional extra" in what seems to be a fairly together life - after their breakup, she likely called some friends over for ice cream and "WTH was with him?", and then got on with things.
She approaches the afterlife as a neuroscientist: her first take is "My brain is dying, I'm clearly hallucinating", and she refuses to take anything seriously until Frozen Yogurt Day. After, Simone thinks "All right, let's kick back and follow the data", spends the next year doing just that . . . .
And comes to the realization that she is a subject in an experiment, one that has not had an IRB within sniffing distance of the place and doesn't seem to care much about informed consent.
(Side note: if/when Simone finds out that she's involved in this because Shaun was using her to get at Chidi, woman is gonna be lit.)
Simone is reasonably sure that the other three are also subjects, notices that the folks who seem to be running it are really amped about this whole countdown thing, comes to the (correct!) conclusion that the experiment is about to end and decides to leg it before finding out what the local equivalent of "Now we find out how the mice's brains have changed" is.
Yes, I wish Simone had helped Chidi pull Brent out of the pit! But I think that as far as she knew, she was running for her life, the man she'd been involved with had told her that he'd been manipulated into investing more in the relationship, and she wasn't willing to sacrifice her chance of getting out for someone who'd never acknowledged her as anything other than a background character in his story.