You state that your cat is hyperactive, that helps a lot in keeping a cat at a more normal weight, believe me. Having more room to run keeps the cat interested in being active. Play time is important as well. If you provide your cat with plenty of toys, such as catnip balls, toy mice... etc., she will likely play by herself to some extent. Also, like kfander mentioned above, cats that are free-fed, meaning the food is always available, really don't eat as much as some people might think. They typically don't gorge themselves, eating only what they really want. My cat can be very hyperactive herself, and has never been over- or underweight. She is perfect as far as I'm concerned... not all skin and bones and not obese either. In fact, she's quite muscular and I would much rather pet a cat who is "firmly" built rather than too thin. I hate touching animals that are all bony, regardless of what the "experts" might think of that condition. If I can feel every bump of the animal's spine, every rib, every joint... I feel like the poor animal is half-starved. I think it would help us help you, if we saw a picture of your kitty. That way, we could better see what we're giving advice about. Perhaps your cat isn't nearly as over-weight as you think she is. Also, remember that, just like people, each individual cat has her own ideal weight that she tends to reduce down to and then she won't lose much more than that.
