i personally would limit the amount that is left down - in fact, there is only one cat in my house who is allowed food down all the time, which is Sam (due to his hyper-t, he needs to gain weight, and he eats in a place no one else goes) . Everyone else has measured amounts of biscuits, although Molly needs to gain some weight, so she gets extra rations. 3 meals of wet plus biscuits is a lot though, so maybe also cut out one of the wet meals, or make hers a smaller portion. Light biscuits might also help. You could also try playing more to help her burn off the calories. It is important to keep on top of her weight though, there are so many health risks when they are overweight.