Switching to a grain free food will help, and this is a high quality food, much better to her. Then don't free feed. Limit the amount put out, and only put it out 2 or 3 times daily. (My vet insists cats only need to eat twice a day, however I have to remind him my cats have not read his books! Three times is required here.)

I switched to grain free 4 years ago, and all the pudgy ones slimmed down nicely, with no effort on my part. All except Crystal, who continues to expand. She currently looks like she swallowed a basketball. Since I have 2 with health issues requiring lots of food, I have yet to figure out how to get her less food. I have increased her exercise. I tried feeding her in the bathroom, door closed, and then picking up all the other dishes before letting her out. That worked for 4 days, until she started "feeling it," and then she refused to go in the bathroom!

With luck, your kitty is not like Crystal, and a few changes on your part will take care of the issue.

The food I use is Taste of the Wild. My cats love the Rocky Mountain formula (venison and salmon) and detest the Canyon River formula (trout and salmon). As a cat owner, I'm sure you have experienced their vocalizations when they disapprove of a food! LOL Here is a link:
http://www.tasteofthewildpetfood.com/products/

You can learn much about cat food by reading some reviews. You / your kitty may prefer a different grain free food. Read some reviews on this site:
http://www.petfoodratings.net/cattable.html

Good Luck! Hey, any chance of a photo? We LOVE pictures, here on PT! LOL