If my wife transitioned, it would be grounds for an annulment
Isn't that only the case if it can be shown that the desire to transition predated the marriage?
My understanding was that these sort of desires manifested themselves from a very young age, which would indicate that they were lying/in denial at the time of the marriage. Is that not the case?
Not all transgendered individuals have a desire to transition.
Plus a lot of people don't have this realization about themselves
consciously until a comparatively advanced age. I was semi-consciously aware but in some degree of denial from the ages of about fifteen to twenty-one, and I have a friend who is about thirty and just starting to wonder things about him(?)self. If I'd had a Catholic wedding at, say, nineteen (vanishingly unlikely in my social circles but still), I really don't know enough about the process of annulment to be able to take a guess at whether the extent to which I was aware of it at that time would have been enough to have the marriage ruled invalid later.