Actually not every brother/sister mating results in puppies that have deformities or even severe behavior problems. It really depends on the parents. I know several litters of this kind where all the puppies ended up normal. How do you think they got so many dogs of one breed? The had to interbreed them. I'm not saying that there won't be deformities,health problems, or behavior problems because there could be. But they still have the chance of being normal. As to the eating...you said you didn't have enough money for spaying so you probably don't have the money for a vet visit right? They don't charge for phone calls so just call them to get their suggestions and if it is very serious then maybe you can work out a payment plan. I've had lots of experience with that.