perents do not always understand such things, the best thing you can do is be the support your friend needs, that includes bingthere for her when she just needs a sholder to cry on. if she realy can admit her problem it may be an idea to encorge her to see a counsler and get to the root corse of the problem, as it sounds like you are both still in education the school may be able to provide it, it is also posible to that her GP may be able to aroange conseling and this shold unless there is emidate danger to heth remane confedenchal.
my advise to you is to stick by her throgh the chalnge which the recovery will present. also try and get you friend to have counsling which is normaly the most effective tretment for belimia. also expect relapses and slipups and just be there for your friend through thich and thin.
feel free to mesage me.