The BIG question is what are YOU willing to do/inforce now that she has broken this boundary. I think your daughter's bulimia is exactly like what we deal with our A's. You are right on with the boundary, but I'm not sure what your consequence will be. What do you want it to be? So now you know she's binging/purging. (Same as any family member finding out their A is active.) Do you kick her out? Do you tell her she must pay X amount for food? Does she use your phone or car at any time? Could you withdraw that priviledge?
As I'm sure you are reading, you know that the only person who can decide to go for treatment is your daughter. All you can do is protect you. I cannot imagine having to make these choices with your own child. I will pray that she decides to get the help she needs. I would actively encourage her to seek treatment. I was bulimic for a couple of years back before I had kids. I was able to stop by myself, but there are still times when I think how great it would feel to purge (sounds insane but it does feel "good" when you are in that space).