Why Ultimatums Don't Work

My wife is becoming an alcoholic. I think it is still in the early stages but it is clear that she has a problem that she will not admit to and that she is very defensive about. To give you an example, when we went to a cottage for a week and she brought 5 bottles of wine and I actually thought that she was cutting down and I was happy. Then later I found empty bottles of vodka that she must have hidden. I confronted her on this but she denied hiding them (but she did) and that she was on vacation and that was why she was drinking more than normal. She was so furious that I would dare criticize her drinking. She always throws all her accomplishments in my face as if that makes it OK. I know at least one of her good friends has mentioned her drinking to her. She used to keep it at home but now when she goes out for dinner or drinks with friends she does not control herself like she used to. It is obvious that she is sliding down quickly. I am at a loss about what to do and we are barely talking because she is so angry with me because I won’t pretend I don’t notice her getting drunk anymore. Now that I have called it out it is like a big wedge between us. I don’t know what to do. Should I give her an ultimatum to force her to go to rehab? I know she loves me but she is so angry and out of control right now I think she might choose alcohol over anything else.