A bitch can become pregnant with her first season which is around 6months of age normally. If she suspects her dog is pregnant she should take it to the vet.
Depending on how far along she is the vet will be able to palpate them, otherwise a scan or blood sample. As stated in last post, bitches can get pregnant on their first cycle, but this is not recommended. Most breeders will wait till the bitch is around 2 years old before breeding, or their 3rd cycle.