That's a tough one. It really shouldn't be on your shoulders, because it's a serious disease. It kind of isn't fair for her to put it all on you, but it IS a good sign that she is admitting her problem. It's the first step to a LONG road ahead, that honestly, you could be there for her, but you shouldn't be forced down it yourself because it can be very tough.
I would keep stressing the part about the therapist. Maybe sit her down and tell her you have been worrying about this since she has told you and that you're very concerned for her health. You could research and list for her the extreme damage that she is doing to her body. Sometimes people need a scare to finally face reaching out to a professional. Maybe gather some stories about ruptured esphoguses and heart attacks caused by electrolite imbalences (talk about tough love, right?)
If you can, look for some therapists in the area and send her the information. Tell her you will go with her the first time, but then the professional can take it from there, and you will feel better knowing she is in good hands.
Finally, don't just forget about it - a lot of people choose to ignore the problem because they don't want to deal with it. You SHOULDN'T have all this pressure on your shoulders, but DO remember to check in with her once in a while, ask her how she's doing with it and if she's getting better.