13.3kg sounds heavy for a 6 month old but they're all different, it really depends how big she is in general. How tall is she? Rodaidh's 3 and a half and he's 13.5kg, he's 15.5" to the shoulder. Pups can carry a bit of extra puppy fat but as they start to get their adult shape you want to be able to feel their ribs and see a waist, as long as you can do that and she doesn't look podgy then I wouldn't worry too much.