Just because she thinks you may have a drinking problem, that doesn't actually mean that you do.
And just because you don't think you have a drinking problem, that doesn't actually mean that you don't.
Either way, her method of trying to fix the problem is ultimately going to fail. You can't force someone to stop drinking by blaming them, or controlling them. They have to want to limit their consumption on their own.
Most of the suggestions so far are aimed at showing her how she makes you feel, by attempting to make her feel the same way. I guarantee that unless she is quite the rare specimen, she will not "get it" and see your point. More than likely it will only serve to increase the friction between the two of you.
My advice is to simply play along and have an "extra" beer once in a while and if she calls you on it, just tell her, "I love that you care about me so much!" and give her a hug. Now you've just associated your drinking an extra beer with giving her love, instead of starting a fight by arguing about it.
And as long as you don't get drunk and stupid, she may not care so much if you have more than 1 beer a day after all.