I have been debating on the same thing with Maddie, she is just a hair under 2.5lbs and will be 7 1/2 months old on tuesday. I wanted to get her spayed before her first heat for sure, and was told that the smaller ones usually take longer to mature. I also was hoping that she would hit 3lbs first. Well my sweet little girl came into heat about 3 days ago, now we are going to wait untill about a month after she is done. If I were you I would try to get her done right arround 6 months, this way she will most likely never go into heat and you can repair the hernia, spay her, and get baby teeth done all at the same time. Also make sure your vet has exp with really little ones.
My vet spayed many of the puppymill puppies from a recent sieze, and alot of those puppies were only 3-4 months and between 1-2lbs. Most importantly you have to feel comfortable with the timing, procedure and vet