Welcome man! And I think i already have the answer for you lol..
The key is NOT necessarily to act like an asshole to her. Although it can work, but that's not what I believe is making her act like this. The key is to act UNAFFECTED by whatever she has to say.
Repeat that to yourself like 20 times. There's really not any need to be an asshole just for the sake of it. (You can neg and play jokes on her to lower her self esteem and stuff, but thats for purpose, and not for just being a dick.)
If you act unaffected by what she has to say, and brush off all of shit tests and whatever else she has to say, then you have a stronger frame. You're showing her that your life is awesome without her and any of her negativity in it. You dont need to chase her shit because you cant be bothered with putting up with that shit
Does this make any sense?
Girls are bitches like that haha, goodluck man!