Hmm, in addition, I'd worry that a growing kitten won't get the nutrition she needs from a senior formula.

What has the vet suggested?

Does she get treats? Those may also be the culprit.

I'm don't recall the history, sorry. Have you tried a better quality food, rather than a grocery store variety? Chicken Soup for the Cat Lover is a high quality food. You can find a place that carries it near you by going to their web site; you put in your zip code. Other high quality foods include Old Mother Hubbard, Fromm's, Canidae, and Merrick. any of these in the kibble form should work fine.

Let us know how she is doing!