Maggie was in a bit of pain the night of her spay and a little quiet the next day but not in pain. She also had 3 or 4 teeth removed. I would ask your vet how he feels about administering the meds to your little one if she is in some pain. Some dogs are spayed later in the day so the vet doesn't want to overdue the pain meds. Maggie's procedure was performed very early in the day so the vet okayed me to give her some more that evening.
As the above poster said, please have pre-op bloodwork done so there are no surprises. Best of luck with your little ones spay. You might also want to check my collars out for helping out with after care of your little one.