Hi and welcome to you and your extra-sweet girl! Pretty overwhelming, huh? It was almost four years ago, but I remember the vet walking in the room saying "Bob has diabetes..."
I thought "WHAT???"
You're in a great place! Full of generous, experienced people who have, or have had, diabetic kitties. All who would be happy to help in any way we can.
If you've poked around much, you might have learned that there are 3 big things we are "big on".
1 - appropriate insulin and appropriate dosing (Good news is that the Prozinc they gave you is one of the insulin types that we consider to be great for cats!)
2 - appropriate diet - we're strong believers in a low carb canned diet. I've seen many folks join lately who are feeding Royal Canin canned.
Did your vet explain why he recommends that food? Most of us feed non-prescription canned pate style food that we can find on the shelves of the grocery store. That saves lots of money if you can do it. And that may solve the problem of your other kitty decided that a "diabetes diet" is now the greatest thing in the world. I fed Bob Fancy Feast classics and my other guy, Mullet, got to share the feast.
3 - Home testing of blood glucose - we advocate home testing using (in most cases) a human glucometer. Did your vet mention that as an option? It saves lots of $$$, because it eliminates the need for future "glucose curve" testing at the vet's office. You can test at home and share the data with your vet.
This is overwhelming at first. The site is sort of huge and there is more information here than any one person can soak in. I've been around four years and I haven't cracked the surface!
Try to come up with some basic questions you need answered. And in the Feline Health forum, you can ask one, two, or twenty questions that you will get plenty of answers to.
You found a great place to be.
Carl