Personally I’d start spending less time with her. That doesn’t mean deserting her. When I have to deal with a negative person, especially a friend, I try to remember Pema Chodron’s advice to look at it as a way to work on the non-judgmental awareness of my emotions and thoughts.

You seem to know some of the reasons for her misery/pain/fears. You might want to use that as a guide in looking at yourself with emotional intelligence and perhaps realizing things about yourself. That way you learn from her rather than having negative thoughts to yourself about her. Chodron is big on looking at situations as teachers.

Kindness, empathy, strength and forgiveness are better and healthier than feeding the habit of negative emotions in ourselves. Now that doesn’t mean I don’t have irrational moments of just not wanting to deal with someone at times and I allow for that. I do try and encourage the positives in myself though. Time will tell how the relationship works out and if you find your way to get through it in positive way, you and perhaps she will just benefit from that.