Having an addicted child can destroy a marriage. Under the premise of "put your own oxygen mask first," you and your wife need to get on the page before you can decide what to do about your son. Would she agree to go to couples counseling with you - preferably seeing a therapist who has experience with addiction? If not, I'd recommend you go yourself.
I can understand where your wife is coming from - this is her child, and she feels if she "loves him enough" she can save him. So- she's ramped up her "caring" to toxic levels...but understand that it stems from her fear that if she doesn't , she'll lose him. Unfortunately, just as you can't tell an addict to "just stop" you can't tell a codependent to "just stop," either.
If your son is using meth, things are very serious. Is she a reader? Nic Sheff's "A Beautiful Boy" details his struggles with his son's meth addiction...perhaps reading it would help your wife understand what you're dealing with. "Stay Close" by Libby Cataldi is a mother's story of coming to terms with her son's addiction. Reading some one else's journey might help her view her actions differently, and ready her to start detaching with love.
In the meantime, you need to focus on yourself, and define your boundaries. While you attend AA, you might also benefit from attending AlAnon meetings as well.