(Getting her out the way quickly)
1) I headcannon that she doesn't like Jeff at all anymore, after becoming more rational she now blames him for her insanity and blames him for her murders. In all truthfulness I'm not a big fan of the yandere thing
2) Since Nina isn't a big fan of Jeff, Jane and her now can stand eachother but they still despise eachother and nothing will change that opinion.
3) She burnt her skin with hydrogen peroxide, her father had a liking for science and left a tub in her room, there was bleach and other chemicals mixed within it too. The amount of toxins did mess her head up a bit too.