you are not responsible for your friend's health and well-being. do what you can within "normal" limits, then let go of it. i know that sounds harsh, but it is not your job to sacrifice your life for hers. what she needs is WAY beyond your control, help, or influence. your life will start to decline if you try to make hers good. because she has these very powerful and difficult disorders, you will never be able to make her completely happy. you will always feel like there is more you should/could do and she will make you feel that way also.
she needs a lot of help from professionals and her parents need to get help for what they contribute to her situation. it is all too much for you, though.
set your limits and boundaries, such as "i will call her every morning and talk for 15 minutes" or morning and evening. "I will go visit with her every other day for 30 minutes." "I will give her 3 compliments and that is it."
when you set limits/boundaries, you give yourself the freedom to know that you did all you could. you also let her know that you did what you could and she will soon appreciate that 15 minutes or 3 compliments more. if she doesnt, that's fine; you will know you did your part.
good luck. i know it's hard, but your life is about you, not her.