
Hi,
Just as there's no 'set' age for girls to reach puberty, there's no hard-and-fast rule for bitches. The average age for the first season is 6-7 months, but just as some will be over a year before their first season, others will be younger. Have you tried the 'tissue test' with her? When she gets up after resting, press a clean white tissue against her vulva. If there is any pink staining or spotting, then she is in season. And if she is, keep her separated from your boy for at least 3 weeks!
Hope this helps.
:)