What a gorgeous girl, is she Persian (or part-Persian)?
As for toothpastes, Logic gel is pretty good. Even though you describe her as laid back I'd be surprised if a cat who hasn't had their teeth brushed before will accept it
The good thing about logic gel is that you don't have to brush it in, even a wipe over the teeth/gums is fine. I used to squirt it on their food, Lu (who is much fussier than Riley) would willingly lick it from the tube but Riley would only take it if it was squirted onto a bit of regular food.
I also used plaque off, a powder that you sprinkle on their food, they were both happy to eat their dinner still so it's certainly not unpalatable.
Talking in past tense here as seem to have slipped off the wagon over the last year or so with regards teeth care but am taking this as a reminder to start the regime up again