Sistersister, I'm glad that you are able to write and ask questions and hope that someone on the forum might be able to give you some useful info. Speaking from personal experience - its tough enough to maintain the balancing act when you're only dealing with Bipolar. Everytime that you add another substance to the mix (caffeine, sugar, alcohol, etc.) it is a shock to the system and makes it that much tougher for a body to attempt equilibrium. I think that the tough love approach is important. Its the whole en-abler scenario and by being supportive in a postive way, it should help to ease her into finding a more healthy approach to dealing with life - not to say that she has to do it alone, but that your relationship is important and you can't allow her treat herself in such a way. She needs to realize that self medicating with all of the other stuff is a sign that there's something she needs to deal with and should seek professional help to figure out a better plan with proper treatment and/or medication
I hope that you are able to find some peace with your friend and hopefully by letting her know that you are speaking out of love, she can realize that you are concerned for her health and want to be a positive influence in her life.