
All bitches are different although often those bred on the same lines tend to come into season at the same age and follow similar patterns.
I've known several bitches be two years plus before their first season and one of my own (obviously immature from day one) youngsters was 21 months before her first season.
Unless you have any other cause for concerns re. her wellbeing I'd not jump to the vets just yet :) Have you spoken to her breeder and established what the pattern is for her bitch line and also what age her litter sisters (if she had any) have broken down?
HTH, regards Teri