17 puppies is an extremely large litter even for an American bulldog!
Generally litter size is determined by the size, health and age of the dam as well as if it is her first litter or not. Dogs between the age of 2 and 7 have larger litters and medium to large breeds have larger litters on average than smaller breeds. Of course there is always an exception to the rule and it sounds like your girl is just that! American bulldogs tend to average a litter size of 8-11 pups.
The main issue with large litters is ensuring that the dam does not become malnourished or dehydrated and also making sure that all pups are feeding well and putting on weight equally. If all this is occurring and they have received a clean bill of health from your vet then I think your dog deserves the mum of the year award and a good pat and cuddle from her human family!