I would try both and see which is more helpful. There will probably be people at each group that are dealing with both issues.
I am bipolar and would be happy to talk if you need. But I don't have the complication of being an addict, thank god, and I'm pretty high functioning, so I can't help with the bottoming out issues. I think most of the books my husband has read have concentrated on living with/having a spouse with bipolar. But my mom liked When Someone You Love Has a Mental Illness. She also felt like memoirs (An Unquiet Mind, for sure) helped give her more insight into how I function.
I'm sorry your family is dealing with this. I'm sure you know, but addiction seriously ramps up the danger around bipolar disorder, so she will need to deal with that as well. I'm glad she's seeking help, and hope she is able to face her addiction as well.
First, major props to you for wanting to somehow support this person vs shun them. I'm not sure where you are located, but I can help find alternative resources around you if you wanna PM. Otherwise, Smart Recovery also has some family resources: www.smartrecovery.org/resources/family.htm