There are arguments both ways with little good evidence to support the strong opinions. In such cases, it is often best to see what your vet thinks and go with his advice.
I would go ahead now, heading off having to go through her season. An accidental breeding and unwanted litter is not the worst thing an inexperienced owner can have happen. Perhaps females are better off waiting to be spayed, but having a litter at 9 months isn't good for them either. Then there are infections and even getting loose and getting killed.
Thanks for that Labman
The vets around where i live will not spay until after the first season. Best to check with your vet and get advice.
I'm afraid a vets advise is not always the best, my vets practically books your pup in for neutering or spaying when you take them for their first vaccinations!
It has to be your choice, don't get forced into it, I usually recommend around 12 months, even if they've had or haven't had a season, just gives their bodies time to mature.