It sounds like I'm trying to avoid the inevitable. It feels weird to just up and cut her off without any notice. But, I see what you're saying. She'll be pissed either way.
Maybe I'm naive in thinking that I can whack her with a small stick rather than a big stick to get her attention. The thing I want to avoid ending our marriage. I love her and know that there's a real person in there still. I worry that going "all the way" will just drive her to do something we will both regret later.
Since I control the majority of the finances maybe a good first step is to just tell her that I won't be enabling her anymore and that she will no longer be able to buy alcohol. It's not hard for me to know when money is withdrawn or when she uses the debit card. If she continues then I can entertain my own account?
Again, maybe I'm being naive but I feel it's right to give her a chance to prove herself especially since there isn't much risk in doing so.