I'm very sorry for the pain your family is experiencing. Children of alcoholics usually are deeply traumatized and that trauma can be buried for a while and then be re-experienced when the alcoholic parent again abandons the child in some way.
It is very good your stepdaughter has returned to counseling, for this wound runs very deep and will affect her for a long time. The wound can create guilt and shame, unwarranted but felt nonetheless by the child, and without counseling, the child might feel guilt about "abandoning" her alcoholic parent when the child sets necessary boundaries. And if the alcoholic dies, without the guidance of a counselor, the child could carry that unwarranted guilt and shame all her life.
You provide her with a stable home and you validate her pain and sorrow and that helps her tremendously, I'm sure. One thing you cannot change, though, is who her mother is and the painful road your stepdaughter will have to be on a while until she finds some peace. That is part of her life. Her mother will always be part of her life, whether they are in contact or not. With help, your stepdaughter can find happiness "whether the alcoholic is still drinking or not" (to quote Al-Anon). And the same goes for you and your spouse. Best wishes to you all in your recovery.