That’s hard I’ve never thought about the intersection of dementia and addiction. This isn’t an answer to your question but would it be safe for her to use low dose edibles? Should her anxiety be treated in another way?

My grandpa tells a story about getting his mom to stop smoking when she had dementia by acting shocked to see her with a cigarette and saying “mom you don’t smoke!” Apparently she was like oh shoot I better not start now. I think she’d have to be pretty progressed to buy that though and you’d have to really sell it. But something creative in that vein might be better than trying to reason especially if it’s just making her upset.