I'd be concerned if it stayed around for a month after spaying, but if it has only been a day, there is every possibility it is temporary. She just might be favoring the leg because stretching it out with walking pulls on the incision. Watch her and take her to the vet if it continues for, say, two weeks.
Did she get any vaccinations or tests at the same time she was spayed? Was she injected with anesthesia? It could be a muscle got nicked or bruised.