How old is she? It sounds like she's quite young, so it's not surprising that she's eating so often - it will stretch out eventually! A lot of bf babies need to be fed every 2 - 2.5 hrs for the first while.
Regardless of her age, you want to make sure she's getting a full feed - do you know about breast compression? It can really help to get the fatty filling milk at the end of the nursing session, fill her up more and last longer between feeds. Also, are you using both breasts or single side feeding? How's her weight gain and is she having lots of wet and dirty diapers?
As for expressing - what sort of pump are you using, or are you hand expressing? It's usually best to pump in the morning, either about an hour after a feed, or if you're single side feeding, pump the other side after a feed.
Once I know her age, it might be easier to figure out some other suggestions too!