And I have just found out that she has fleas she has had them before because of our other cat coming in and out I'm just wondering with her having fleas will this cause her operation to be cancelled? As I no she gets very bored being inside and I would love for her to start going out soonx

It shouldn't. They will probably have to treat her for the fleas, but they should be able to go ahead with the surgery unless she is TOTALLY infested.