This is a topic of great debate among vets and you may never get a definitive timeline. However, most are in agreeance that you should have the surgery performed before the first heat cycle (4 - 5 months old). Spaying the animal before the first heat cycle lessens the chance of them developing breast tumors/cancer.
Spaying is more invasive than neutering so unless your have a pressing reason to have her spayed, you should probably wait. It's actually the anesthesia(sp?) that is the risky part. Have you asked your vet? My old vet reccomended around 4 to 6 months. However, he bred Siamese cats and altered the kittens before sending them to their new homes at 8weeks with no problems. My own two girls were spayed at approximately 6 months. Good for you for having her spayed.
We all seem to have overlooked the vaccination part of the question. Your kitten should have the FVRCP (distemper etc.) at 8 weeks with a booster at 12 weeks and 16 weeks. And the rabies shot is given at either the 12 week or 16 week visit. Mine waited until the 16 week for that because they are very small cats. If she is an indoor cat, that's all you need. If she goes outside, your vet may give vaccinations for FIV and FELV also. Once your kitten sees the vet for the first time, the vet will normally tell you what is due next and when to come back. They will also advise you on when they recommend the spay visit.
My vet has a weight requirement for spaying and neutering. 2.5lbs for females, 2lbs for males. Each vet is a little different. The same with shots. Talk to your vet, he will tell you which vaccinations they need and his requirements for when he will spay her. KUDOS to you for being a responsible pet owner.
I like most cats better than I like most people. I'll try to be nicer if you try to be smarter.
I just got 2 new kittens from the shelter. One had just turned 3 month & the other had just turned 2 months. They were both already fixed by the shelter. When i took them for their first visit at the vet he said that was fine.