Hi there...
I think that the doctors would already have a good idea, if she's been admitted to hospital. In my case it took years, but only because I'm a crafty so and so, and hid my crazy from people as best I could. My family thought I was odd, but didn't know the extent of it, until relatively recently. I'm thirtynine, and schizoaffective. (Similar to bipolar, with some schizophrenic symptoms.)

My relationship with my Dad was very poor for years, partly due to my illness... it's possible that your daughter's acting out is a symptom of her condition. It's also likely that her drug taking is "self medicating", that is, she takes the drugs to manage her moods, rather than just "get high." I think the relationship between drug abuse and bipolar is complicated... it can excacerbate it, but also be caused by it. In my case I drank to shut myself up. Thank God I didn't get onto other drugs... I go psychotic quite easily, and my experience of other drugs, even as "soft" as marijuana scared me away from them quite effectively. Booze was another matter, so I understand how someone can hide in substance abuse to feel normal.

I would say that you are doing the right thing. You love your girl, and always will, just as my Dad loved me, when I was being, quite frankly, a "b!tch" to him. Since I've been medicated we've repaired our relationship, and it's my hope that you and your daughter can do so too. You may have to accept her being a prodigal until she realises herself what she needs to do. I hope you don't have to wait as long as my poor father had to.