How are her diapers? What # of wet and dirties is she having each day? Some babies just gain weight slowly. Someone has to be in the first centile, if that makes sense. Being small isn't necessarily a reason to top up.
Are you feeding on demand? I would say that every 2 hours at 9 weeks (from start of feed to the start of the next feed) is actually a longer interval between feeds than average. You'll find that lots of babies are still nursing more frequently than that at that age.
I wouldn't try to increase the time between nursing sessions, especially if you're worried about weight gain. Just feed on demand at the early signs of hunger. Rooting, turning head from side to side, sucking on their hands, smacking lips, etc. Pretty much any movement for us at that age meant he wanted to nurse. It's really difficult in the beginning because it seems like you're just nursing all the time, but I promise it gets easier. She'll eventually learn how to nurse more efficiently and you won't be stuck on your bum quite so much.