I have a large Gundog breed and that would be fairly common for my breed. One of my girls was 18 months old before she had her first season, then went 13 months till the next and the last one was 11 months later.
Her mother had her first season at 9 months and then every six months after that give or take a couple of weeks.
Having been stressed myself about seasons I asked a few other breeders and they said it was very common for some dogs to have a season only once per year. It makes no difference to fertility, as a half sister to mine,who also has a yearly cycle was mated and delivered 13 healthy puppies.
I am not sure what a vet could actually tell you without extensive exploratory procedures' which would probably need to be carried out by a specialist.
If it were my dog and the girl was fit and healthy, I would just wait and see, she has already had one season so you know everything is normal there.
To be honest I see having a yearly season as a positive advantage for a show girl. I do not lose entry fees, or have to miss shows due to a season, and she does not drop her coat as often so a win, win, all-round.
To be honest I think with bitches and seasons there can be quite a wide variation even within breeds. I had five bitches in my last litter and they have all had different patterns.
One of my friends has a Flatcoat bitch and she was also quite late in coming into season, at around 20 months and also goes long periods between seasons, but she is dual purpose girl and in very hard condition.
From just doing asking around other breeders the general consensus was that working bitches tend to have less seasons.
Perhaps some Lab breeders will come on and say what is usual for the breed.
By goldie
Date 07.07.13 21:55 UTC

One of my girls a GR who is now 6yrs old has only had 3 seasons in that entire period of time, her first season was 19months.
My vet told me when she was 3yrs old they would investigate further if I was wanting to breed from her but I don't breed myself.
He said she would be having silent seasons and unless I was concerned about her health then best left alone in her case.
She is being spayed after her next season when ever that maybe.