Sorry, Kirsten, all I know about diuretics is that they do flush out the water in your system, and it sounds like maybe Luna was retaining a lot of water. I do know (from personal experience) that retaining water does make you look puffy all over, so that could be why she looks thinner - even in her legs.

I don't know how long diruetics stay in a cats system, but I would say if the trips to the litter box have slowed down to a normal pace, that's probably what it was. I would definitely keep an eye on her and call the vet in the morning.

All fingers crossed that her kidneys are ok.