Sounds like she is having a phantom pregnancy. The best thing you could do for her is have her spayed after this season. She is still young enough to benefit from the op and it would make her much happier.
As for the food - tough love

It sounds like a behaviour thing if she still has an appetite for scraps and hand fed stuff. So if she was mine I would pick a dry food and stick with it. Put down a small amount for 15 minutes then take it away and give nothing else until the next meal time and again, only leave it for 15 mins before taking the bowl away. If she is healthy and she is being offered appropriate food she will not starve. If she is not healthy you need to get her to the vet.