Yes, take her to the hospital before it's too late!
Your friend is extremely sick and keeping this a secret is not benifiting her at all.
Please talk to your friend and tell her that she needs to get help as soon as possible and that you're not just going to stand by and watch her do herself this harm anymore... tell her she NEEDS to talk to a professional about this - offer to go with her if it will help. However, if she refuses, please talk to your school guidence counsellor or a teacher or your parents - ANYONE that can get her the help she needs.
Her bulimia doesn't sound at all 'mild' anymore... I would say 'deadly' would be a better word to describe it now. At my own worst my BP was 50 and I was VERY sick at that point. Your friend is too. Please do this for her... she deserves to get better from this.
Take care and good luck with everything! Let us know how things go, okay?
Ashlee