This might be a daft question, but during the day, are you allowing her to feed for as long as she wants to or are you determining when a feed should end/you should switch sides? Also, often LOs who are BF do need to nurse more frequently than every 4 hours because breast milk is digested rapidly. And some mums NEED LO to feed more often to maintain a good milk supply. The more frequently the breast is emptied, the more quickly milk is produced.
Also, have you tried breast compressions when she seems to be coming towards the end of the feed to keep her interested a bit longer and to get some more of the higher fat milk from the breast?