I'm guessing she heard or read something recently that popped the idea into her head that had nothing to do with you.
maybe heard from a friend that their spouse had relapsed, or read an article about people slipping during the holidays, or something in a movie or book about a person slipping or about spouses and trust or any one of a hundred different totally innocent things.
I know I've had a spouse or BF ask me stuff out of the blue that was totally "where did THAT come from?"...and I've done the same to them and it was nearly always triggered by some random thing read, heard etc somewhere.
Just the other night I asked my BF what he'd think if I did thus and such, and he said "Why would you ever want to do such a thing!?" and I said, I didn't, I was just wondering how you would react...just because I'd read something online.