
I wouldn't worry, unless there is anything obvious wrong with her, one of my girls was just 2 years old before her first season, then 12 months later had her second, she was mated on this season and gave birth to 9 very healthy pups, all survived.
We had the full blood works done at the vet, all came back clear, he said there were further tests we could have done, but suggested leaving it until she was around 4 years old if nothing had happened, the tests were expensive and he didn't think she would need them done, typically 2 weeks after having the blood tests done her first season arrived.