If she is one year old and has just recently been spayed then her hormones may previously have been suppressing her appetite and she had other things on her mind that were distracting her. It is important not to overfeed her as, as Rosella says, cats tend to gain weight after spaying anyway. This is simply because if they are eating the same amount (or in your cat's case more) as usual, when they no longer need that many calories to keep them going, then of course they gain weight. If the problem is recent, I suggest you speak to your vet - the operation may have pushed a formerly latent problem into action and it is important to see if that is the case so it can be treated. Please don't give into her demands for food - obesity is very bad for cats. If she is a normal weight, then normal feeding will be more than enough for her. When she is demanding food try distracting her with a game - a feather on a stick or similar that you can use to lead her away from the feeding area and keep her occupied.
