Roommate may be bulimic... what to do

This morning when i sat on the toilet seat for a pee, I was discussed to find throw-up chunks on the front edge of the toilet. There was also some nasty throw-up juice on the little rug in front of toilet (which is now stained). I plugged my nose and decided to not look at it-as I went for some toilet paper, there was ALSO a chunk on the toilet paper too. It was gross.
I assumed it was one of my roommate's boyfriend since he likes to get drunk, etc. Anyway... it turned out not to be him. Which led to the only other possible person- my other roommate. I talked about this with a different roommate and she told me that she had been hearing this girl throw up a lot recently. I actually heard her throwing up during the afternoon today. After she finished she took a shower and I waited for her to come out and get dressed. I heard her go to the kitchen and I asked how she was feeling. She said she was fine except for her cough/throat. I mentioned the fact that maybe she has a stomach bug and she said no and didn't get my hint that I heard her puking.
She is an extremely isolated girl and I never see her eat, but I know she does eat random things at odd times inside her room. I am not that close with her (because she is always inside her room with the door closed) however I know her well enough that I want to help/care. I'm just a little nervous about how to approach the issue and what to say-I have an idea but don't want to act too soon.

Any help? Thanks!