It is true you should never breed from dogs in their first heat. However, ideally the minimum age for breeding is 2 years. This is to assure that she is fully developed mentally and physically and any genetic defects she may pass onto her offspring have had time to surface. Breeding under 2 years increases the likelihood of a Caesarean birth which is costly and poses certain risks, and it also increases the chance of the puppies being rejected and mismothering.
She can get pregnant the 1st time she goes in heat which occurs between 6 to 9 months of age. It is not recommended or safe to breed her until she is over a year old.