What happens as a result of her drinking? Perhaps it might be a good idea to focus on how you feel as a result of your wife's behavior rather than on trying to prove that she has been drinking. Some ideas: Is she honest? Is she clean? Does she drive a car after drinking? Does she shout? Does she get aggressive? Is she irresponsible at times? If any of these apply, then, how do you feel as a result? What boundaries could you set to protect yourself from such behavior?
One of the things that used to drive me crazy was that my AH had a totally different idea of reality. What he saw as blue, I saw as green, etc... What I've had to learn is to trust my instincts and my view of reality, and not let myself get influenced by him. In order to do this, I found it valuable to go to Al Anon meetings, where people did not judge, but supported me and my views of reality. Alcoholics have a way of making us feel crazy!