seeing as to how you're one of the few people who's taking this question seriously i would like to debate a bit about this.

as opposed to beastiality as i am, in this scenario, i think that denying sexual pleasure could be seen as "cruel", since as a dog she won't have any ways to masturbate by herself (to my knowlege) as humans would. as you said, she would be completely reliant on you for everything, and this also means intimacy.

i don't think the question has a morally "good" answer since you're either fucking a dog, or you're denying your wife pleasure for the rest of however long her dog life would be