It's scary, I know, but getting hungrier is good! It means that your metabolism is going back up, so you can actually eat more without gaining any weight! It is a very normal and human thing.
As for the counseling, I went the first time and it was a little hard. I think the first time she just asked some questions and stuff to kind of get an idea of where I was, what I wanted etc. A tip- it's a lot easier in the long run if you just make yourself open up, be talkative, and tell all the first time that you go. It's hard, but worth it.
Sessions can be as long as you schedule them for. They're usually either 30 minutes or 1 hour. Mine are an hour. It seems like a long time when you go in, but once you get "warmed up" and start talking it goes by really fast.
Don't expect to notice things really quickly. It takes time to change your thinking patterns. I think that there's a law that the counselor can't tell your parents stuff unless it's life threatening, so don't worry about telling her stuff. It took some time, but I told my therapist how I eat, what I eat, what I do to throw up, how disgusting I am, etc. And guess what? She still talks to me perfectly normally and is very much a friend to me!
A note though, all therapists are different. They are human, so there are different personalities, styles, etc. If you just don't 'click' with your therapist after a couple of sessions, tell your mom that you would like to see someone different. Many people have to try several therapists before they find one who matches their personality.
Anyway, tell us all how it goes, okay? When is your first appt? I'll pray that it goes well!