dining with dieters

I don't know whether this is the right forum to ask this but since I'm already registered, I thought I'd ask here. I catch up with a certain friend sometimes, and we always go to a restaurant at her suggestion. I don't know if she's on a diet or what but almost every time we go to a restaurant , she would eat like 5 bites and say she's finished. Seriously. The first time we went out to eat , I realized after a while that she wasn't eating at all. Why suggest going to a restaurant if you're not going to eat?

One time I saw her eat lIke a normal amount that people would eat (I realize "normal" is hard to define, but it was more than 5 bites) and she said she was being "bad" (her word) for eating "so much." I mean, does she have an eating disorder ? She's so skinny, she must weigh 90 something. I am not exaggerating.

We've gone dining several times and it's gotten to the point where I want to scream at her to eat something or just not dine with her anymore. Am I being unreasonable? I was thinking this must be like how guys feel when they're out dining with a girl who will only eat a salad ( except those girls eat more than my friend) while the guy eats a big juicy steak.

What do you think? I like catching up with my friend but can I tell her I won't go out to a restaurant with her unless she eats? I mean, really actually "eat"? (more than a few bites). Should I ask her if she has an issue with eating? Should I tell her she's so skinny she can afford to gain weight? Thank you for any insight.