
I have toy breeds, and wouldn't have them spayed when pups are 8 weeks. My toy breeds still have milk at this stage.
So I agree with Brainless, wait an extra couple of weeks. Never have a bitch spayed when she has milk, even if it is a phantom pregnancy.
If she isn't pregnant, then mid way between seasons is the easiest. There are far fewer blood vessels for the vet to tie off when they aren't raging with hormones. If it's easier for the vet, that makes it a quicker operation for your girl - and less anaesthetic required.