I agree that exercise is the best thing that your cat can do to lose the weight. When I lived in the apartment, my cats basically just ate and slept. One of them was especially overweight and another one might have been a little overweight, but it was hard to tell because he has such long hair. Anyway, since I've been out on the farm, I let my cats outside for about an hour every day. It didn't take long for the cat that was overweight to lose those extra pounds. She is 10 years old this year and I know that she is healthier now because she gets to exercise and she doesn't just lay around. I have always kept dry cat food out all the time for my cats and I let them eat at will. They each just nibble on a few pieces at a time throughout the day and I've never had a problem with just one of them eating it all up. After they come in from playing outside, they all get a treat. I split a can of wet food between them all, so they get their treat, but they don't get too much at a time.
I think if you could spend some time playing with her every day, this would help her to lose the weight. Since you say you don't play with her much because of her sharp claws, you can get one of those cat toys that have something dangling on the end of a long stick. I don't know what these toys are called, but the cat will bat at and play with the toy at the end of the stick and this will keep your hands away from her sharp claws.
