DIET.

No free feed; get a measuring cup, read the amounts on the bag, and follow them to the letter.

Putting a round cat toy in the dry food can slow down how fast she eats. Also - watch the wet food, if you use it. Very high in calories.

Grain-free food might be an idea, as there is less "filler" and kitty will feel full on less.

Best of luck and I hope your girl feels better soon!