Well, pain is pain no matter how old you get it done. I do know, though, that my vet absolutely, positively will NOT do it to a cat over 6 months old, and will try to talk people out of it before 6 months. Declawing is really a very extreme measure - it is amputating their first knuckle. This is no manicure!
Have you tried trimming the kitten's claws? Asked about SoftPaws (they are nail caps for kitty that make the claws dull, and they come in cool colors too!)? Do you have scratching posts for kitty for her to dull those little claws on? There are a lot of alternatives to declawing that will keep kitty whole and you a happy kitty owner.