I agree with Flutter--While there might be some post-partum depression going on, you also said that she had an alcohol problem before she got pregnant. When we stop drinking for a time and we go back to it, it's often worse than it was when we stopped.
Make sure her doc knows about her history--that this isn't a recent development.
Often, with sobriety, depression lifts significantly.
Keep us posted, we are all pulling for the three of you.