Lu got her operation at 6 months exactly, it just happened to fall on that date. The poor girl was very sore for a while, so we just put blankets on the floor for her to sleep on since she couldn't climb into her bed. She was in the 4lbs range also when it was done and everything went fine. The vet said her bits were the size of a small cats!
She also had a couple of baby teeth removed. That didn't seem to bother her at all. She had to go back a couple of months later to get 2 more baby teeth taken out but again, that didn't seem to phase her.
Lots of TLC and your little girl will feel better in no time
Good luck to her!