For future reference, cats do not need to have a litter before being spayed. It's best to get them done before their first heat cycle, kittens can be done once they weight 2lbs at around 8-10 weeks old.
Shonk, it isn't better for the cat, and could be worse - she could have problems giving birth, and you are letting her go through the pain of mating, pain of giving birth to take them away from her. They dont have maternal instincts like we do, so dont feel the need to have kittens. I have had so many mum cats who have been so much happier after the babies have gone and they have been spayed.