No it's not dangerous to have your cat spayed. Actually, it would be in the cat's best interest to have her spayed. Females that are NOT spayed have a very high chance of pyometria, a uterine infection that is fatal and can kill your cat. There aren't any side effects to having a cat spayed. She will have stitches when she comes home and be a little groggy from the anesthesia, but that's about it. She should bounce back within 24 hours.