Your wife is being way too precious. If you mom is an innocuous drunk, I see no reason why you can't visit her while you are fully present and fully in control. Sounds like your mom has exhibited enough control over the years for you not to have noticed? Surely, I do not condone functioning alcoholism or alcoholism in general, but if your mom is not a daily fixture and your daughter does not seek to emulate her, I see no reason to exacerbate the situation by further conflict. Go there, visit, supervise your daughter and if the drunkenness ever makes your mom act threatening, rude, disturbing, etc., that's all she wrote and your mom loses her chance. Your mom can't hold the baby while drunk, etc. Trust me, the baby is not going to be damaged by seeing what you didn't even realize until two years ago was drunken behavior.
It's not the end of the world to be around someone who is drunk--you didn't mention that she's out of control, fighting, hitting, violent, etc. If she isn't babysitting or having one on one time with her or giving her cooking/driving lessons, what's the big deal?
I say this as a former alcoholic, who, even while drinking and managing my son, never allowed him to be babysat by anyone by us throughout his 9 years of life. I'm very protective of him and there are people I don't allow him to be with who have no problem with drinking, so I'm not advocating this because I'm lax.