HI - you really need to speak with your vet who can prescribe a diet based on her exact weight and how much she needs to lose.
My cat has just started kitty weightwatchers at our local vet - the service is free but they weigh her and go through tips to get her a bit more active i.e. putting her at the bottom of the stairs and then feeding her at the top so she has to run up.
Queen cats (i.e. females that have been spayed without having a litter are notorious for carrying extra weight) especially if they are house cats. My cats baggy belly is testament to that. Along with her pattern of sleep, eat, sleep, 2 minute burst of exercise, sleep, eat etc
You have to be very careful about weight loss in cats (more so than dogs) as if they get too little nutrients or the wrong type it can cause them more health problems.