Thank you so much for the reply....I don't think that I can ask how I can help her as it took a great deal of bravery for her to tell me that she was...
Before I found out, I "mom-ed" (like I do all the kids that come into my house) and tried to get her to eat. But in my defense I had no idea.

She leaves my house before dinner (my son says that she doesn't want to eat in front of people) so I have suggested to him that they take their plates upstairs and eat there.

I simply tell her she's beautiful (she is) because she's not, to my eye, underweight (she doesn't cover up with baggy clothes).

I will ask her if she is aware of when she's slipping....and then come back and ask for your help again if it's okay.

I am sorry I didn't get more responses, but yours was most helpful. Thank you