Is she a giant breed? Just asking as I had to wait for my girl as well, and she is. My vet suggested spaying her at our first visit, but when I explained my reasons, while she didn't totally agree with them, she was very nice about it and didn't withold anything. They're finding the automatic "spay/neuter a.s.ap." isn't right for every breed. You might want to find another vet who is more receptive.
And I think it's 3 months. But I would check with your breeder.