Then it could be something hormonal? Cystic ovaries? If she is already three...she must have had more heats then 2? I suspect she may have had silent heats. Most bitches have a heat before the age of 1 year, and then every 6 months after that. If her heats are this irregular...then there could be some underlying problems. I would get in touch with your breeder and ask about this...often the dam has the same cycle as her female pups.