I would say 18months..GSD are a large breed and need to physically mature first..
(or depending on when her first season comes, as close to 18 months as possible, allowing for half way between seasons..does that make sense?)

Hi Melsgems I would go for three months after the beginning of the first season, so for most bitches that is midway between two seasons. My vet also prefers to do it at this time when the hormone levels are reasonably static and there is less chance of hemorrhage.

I understand if you spay bitches too early (and this applies to some breeds more than others) there is an increased risk of urinary incontinence.
What does your vet say?

my vet recommended 6 months,we did on our gsd bitch with no problemsxxx

my puppies have all gone with advice on spaying after a vet told one buyer that he's book the pup in for spaying with the second vaccination
I know advise they let pup have at least one season first and then as others have said about 3-4 months after book in for a spay.

I always spay bitches large and small at 6 months now and all have grown quite normally and turned into lovely dogs. I also castrate males at 6 months too and they always grow perfectly normally.
I never used to spay or nueter many years ago that young if at all after hearing all sorts of stories, but moving to an area that has a high number of loose latchkey dogs I had to for safety and I have never looked back and wish in many cases I had done it before.

I think the honest answer is - depends on the dog! Breed, size, temperament, circumstances should all be taken into account. Neutering can sometimes affect temperament so I would say if a male is nervous or a bitch is aggressive, don`t neuter until you`ve addressed the behaviour. This isn`t an arguement for not neutering, by the way, just for delaying it.
Re. the long bones / growth plates - it does / can affect male dogs.
The trouble with seeking advice on neutering is that it tends to be presented by pro- and anti- factions and a lot of the research I`ve read isn`t particularly conclusive.

her temperanment is great, so no concerns there. I just want her to be able to grow and mature as she should. Vet prefers to do after first season but can be flexible.

A part of me wants to do it ASAP (so that its over and done with) another says wait let her mature first......

Thanks for all your advice, I think I will wait till her first season comes and work from that

Mel x