I decided on the food myself. My vet didn't tell me I had to do any particular feeding schedule, but I also didn't ask them about it. I just went with what I thought was best based on what I've researched. Socks is the same way- he'll eat anything he sees on the floor without checking to see if it's food first! With Kit's diabetes not regulated, it's likely she's extra hungry because they can't process all the food they're eating, so it's possible she needs more food than usual until she gets more regulated.
It's hard, but you definitely have to be patient. If you rush things, you could just end up going backwards and take even longer. But it's so HARD!! I'm glad Socks' black numbers turned out to be "good" for something at least! Haha
I did the switch to Fancy Feast gradually, then went back to DM (that's what my vet originally recommended) when I got some bad numbers since I wasn't sure if that was related, although looking back, I think it was just a coincidence. The switch from DM to Tiki wasn't so gradual. I was working on switching him over, then he had a bad day where he wouldn't eat much (which is SUPER weird for him- he always wants food, any food). He didn't want any DM and he finally started eating some Tiki, and I haven't fed him anything else since.