5lbs sounds about right. Kubrick was 5.75lbs at 13 weeks. As far as how much to eat, make sure to feed her 3x a day and just follow the instructions on your food bag as to how much to feed a 5lb dog. As she gains weight, you will need to change how much you feed her based on weight. Also, eventually she should stop eating her 3rd meal regularly. Once that happens, it's time to go down to 2x a day.