I took the time to read the whole post and scroll through the comments and one thing has concerned me across the board. Has nobody thought to consider this 'problematic friend' needs mental health assistance? Now I'm in no way saying it is OPs burden or that you owe her anything at all but I'm disappointed in the lack of consideration of the possibility.

Reading this part, for example:

She is very...intense with school, us, her career, etc. She has no friends from high school, even though she lived very close to her school. She also has no friend group from University. She just had her boyfriend, who she broke up with a month ago. These should have been red flags.

Having no friends may be result of her behaviour (or a result of past abuse and/or mental health issues) and her behaviour is likely being compounded by people not having the courage or compassion to honestly speak to her about her behaviour. Even a simple "I've been thinking about our recent chats and I'm worried about you." opening line is an icebreaker. Either she gets aggro because she's just an insecure drama queen and the already fragile relationship is ended or she breaks down and opens up because somebody finally took the time to find out what is wrong with her.

Either way, an honest discussion needs to happen. No lies or manipulation from either side.