I think my friend may be bulimic?

So my friend is like really skinny but doesn't find herself pretty. Since the beginning of the school year my friends and I have noticed her and this other really thing girl have been going to the bathroom after lunch most days. They are there for about 10-15 minutes. When they come back their chewing gum. Also her teeth are really yellow, like I'm disgusted by it. I think in health we learned about how it can discolor the teeth. she's also has been having even more mood swings, like really happy or really miserable type.

Have you or anyone you know been bulimic? What are the signs? Does this sound like bulimia to you or am I getting paranoid?

Thanks!
I think my friend may be bulimic?
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