I would think that if your friend was admitted to a psychiatric hospital, it was probably of her own free will, or did she threaten her own or someone else's life? If she made the decision to go there, then I would think that she has accepted that she has a real problem, and needs to deal with it when she gets out.
Hopefully, either way, she has a strong support system including family and friends that can help her through this. She's obviously lucky she has you. It's not uncommon for us to be in denial in the beginning that we really need to be medicated and that we are really that sick. It can be a hard thing to accept.
How willing she is to talk about her condition will depend on a lot of things, how comfortable she is with you, and her acceptance of the situation, and how stable she is now that she's been through such a hard time lately.
I had a long manic episode about a year and a half ago, and I really just needed mellow, quiet time to recover, and try and wrap my brain around everything. I didn't really want to talk to any of my old friends, or do much at all in the beginning. It's really hard to say how she may react.
Any of the threads on this board from either Angelblue or Colefort might be of help to you, they are both in relationships with bipolars, and struggling with some of the same issues you will probably be facing.
Good luck to you and your friend, come here anytime, it's a great group!