I am so sorry you are going through this. I will defer to others here about your questions about what to expect during and after rehab (my qualifiers never went, I divorced one, one passed, and I left one). It's sad to say but yes, continuing the divorce process might be the best thing for you, your finances, and possibly even her.
I would say it's really good you've reached out for support. It really affected me emotionally, and I don't have to talk to anyone while I'm working, so I can't imagine attempting to be effective at sales with all this going on. If you can find either an in - person or online AlAnon meeting, that could really be helpful. I have found this forum to be of great support also, even the painfully honest comments pointing out my codependent behaviors.
Your step - daughter might also benefit from AlAnon and / or ACOA (adult children of alcoholics). While you have been listening to her vent, I would suggest that you encourage her to try one of these groups. I've found because alcoholism, addiction, and codependency are so enmeshed in my family of origin (FOO), that venting turns into a messy, enabling, codependent drama between family members (and of course, beyond a just - the - facts conversation to keep her updated, it might not be a good idea for your to vent to her about this whole thing).
Your younger daughter might benefit from AlAteen, and though I hate to mention this, if there's any question in your mind about if your wife was drinking during pregnancy, you might want to get your younger daughter screened for fetal alcohol syndrome (FAS) especially if she has had any learning disabilities or behavioral challenges. She is older, so it's not quite so critical but it could help put the puzzle together if there have been any developmental challenges.
I'm glad you've been reading everyone's stories here. Keep reading, check out the stickies and the resources. It all helps when attempting to understand this completely incomprehensible addiction.