Please diagnose this.?

I just found out that my girlfriend has somewhat of an eating disorder. She eats regularly but after she has a big meal (dinner), she doesn't feel good until she throws up. She has been doing this almost everyday for the past 3-4 years and she is 17. She claims that she stopped about 2 months ago but I am still very worried. Can someone please help me diagnose this and tell me how to get rid of it. I am extremely worried and will greatly appreciate any help.