Help for my sister please eating disorder and more

My sister who is 48 has a serious eating disorder / problem of some kind. She was over weight for most of her life, then, started drinking this powder off the Internet only, and lost so much weight see looks like a skeleton. Then, for 3 1/2 years, she stated and believed that she could only eat chicken broth with purred cooked zucchini. The past 2 years, she's "found" and decided that she can eat sauteed chicken breasts pieces with cut up yellow squash. She does eat baked chicken wings from only one restaurant because the rest of the chicken wings in the whole world are "bad for her."

She grew up eating all kinds of foods and continued to do so for many years of her marriage. But these last years, she believes these warped ideas and has convinced her whole family & my aging mother that she can only eat these few things because of all these different medical problems she claims to now have. She's like a hypochondriac with all of her supposed problems why she can't eat food. She doesn't believe in Drs. and claims to have all these supposed medical conditions now. I KNOW that she also has some psychiatric problems, but, none of the family sees this. They believe every warped thing she says and they are convinced that she can't eat other food too. Even all fruit is "bad" for her and she can't eat it ever. She has gotten very good over the years at convincing the family of "strange beliefs." For years, she's also been taking coffee enemas twice a day. She also believes that everyone should take 18 - 20 colon cleanse tablets every few days (from the health food store). She claimed over and over that it's good because when you take those colon cleanse tablets, it not only cleans out your entire system, but, she examines what is there when she goes to the bathroom and brags about losing stomach and colon linings and thinks this is the best thing.

I don't know what to do about all this. When ever I express a mild opinion, she gets highly upset and takes refuse in her room and takes her family with her. I've tried talking to my 86 year old mother about this, but, my sister has her convinced of all these wrong things and my mother defends my sister and gets mad at me. I"m the wrong, & unwanted for not falling for my sister's crap. My sister needs serious help. She claims Drs. are quacks and that they don't know a thing.

What can I do to get through to the family about the fact that she is sick in the head with these examples and many more not mentioned here. My sister is not well mentally and can't handle it if i ever say anything other than agreeing with her.

Do any of you have any suggestions? Please help me.
Amy