Sometimes it takes being around a person like your friend, to work toward positive changes in my own life. I can relate to your story in some ways, because i rent a space from a "friend" who i consider the most pathetic, self-indulgent complainer in the world. I'm so tired of hearing about how her life is miserable, and she does nothing to improve it. She has a home, a husband who buys her anything she wants as long as she whines about it for weeks on end, she can go out anytime she wants, she and her husband seem to have a good relationship and are best friends. She is mean-spirited toward others, says whatever is on her mind whether it's insulting or not, is critical, judgmental. She has some physical problems but won't have surgery (her back), so i have to hear about that! She says they "can't afford it", but they have great health insurance and her husband has money. She also has no friends except one who lives 500 miles away (who only remains her friend because of the distance).
It's come to the point where i avoid her. And i have also taken a good look at my own life, and decided i am more content, settled, accepting of my life than she is. I am not married, struggle for money, have an older car, etc. But i work like crazy on my art, and i get out there and do the things i can afford to do. I also take care of my health. I was in a serious car accident, and yes i suffered for years, but guess what? I never gave up.. i worked hard to walk again and now i hike all over the place, just like i used to!
I suppose we can both be happy that we aren't in the same mental and emotional position as our friends are in, today. When your friend complains show empathy, then change the subject or just get up and go find something else to do. That's what i've done, and my friend over here doesn't bltch and moan quite as much as she used to....
i hope your friend gets a diagnosis and that she will work toward her own, positive life changes.
take care.