Welcome and glad you have found us!
Alcoholism is a disease of denial. You see if she admits she has a problem then she has to do something about it. Its not just other people they deny it to - its can also be a battle within themselves to "prove" they don't have a problem.
The behavior your wife exhibited when you confronted her I would call blame-shifting (its your fault not mine) and gas lighting (I don't have a problem you are the one with the problem you are crazy) common ploys of addicts.
P.S. Threatening to become an alcoholic is a unique threat I have never heard that one before.
Whether or not she is an alcoholic I don't know. What she does have is a problem with it, you have a problem with and the family has a problem with it. Her reaction is not a good sign at all. Alcoholics will protect the alcohol first.
You did not cause this. If your purchasing alcohol resulted in alcoholism you would be one yourself.
Stick around and read as much as you can. Post often. Sorry for what you are going through it sucks.