Great job on helping your cat lose some of those extra pounds! I bet she feels much better.
Unfortunately, your cat's skin will not likely tighten around her new body.
PEOPLE: For, people, it can take a couple years before the skin "fits" right after weight loss...and that's only if you are young and didn't lose too much weight. People not in this category often choose surgery to tighten the skin.
CATS: It is similar in cats. A cat's skin elasticity gets less with age. This starts, usually, with middle age cats (i.e., your kitty). If a cat loses weight too quickly, this can also cause large amounts of skin. In this case, the skin's elasticity just can't keep up with the weight loss.
WATER: One thing that will likely help increase your cat's skin elasticity is plenty of water. Inside cats tend to be dehydrated. So, we need to entice them to drink more. If you are able, get a cat water fountain. My cats love ours and drink a lot more water than without it. If you cannot get a fountain, leave a faucet dripping in a sink or bathtub.
I had a similar situation with my middle-aged cat a few years ago. He was only slightly overweight. When he lost a couple pounds, he had stomach fat that almost touched the ground, and he never lost it. However, he was a happy cat. As long as it isn't bothering your kitty, she should be ok. Ask your vet next time you're there to see if there are any other recommendations.