Are you sure she has an eating disorder? Could it be morning sickness?
When you have an eating disorder it is very difficult to control your behaviour around food even if she is pregent. I think the best thing to do is to get her to see her doctor because there could be a lot of damage done to her and the baby if she is bulimic.
However she might not have an eating disorder it could have something to do with morning sickness but either way if you are worried then I really think the doctor is the best option.
Let me know if you have any other questions and i'll do my best to answer them.
I hope everything is going well.
Take care!