If you're getting lots of poos (better indicator than wet nappies in the first month or so) and good weight gains, then should be fine. How many feeds is she having in 24 hours? Generally like a minimum of 8 to ensure you establish a good supply. It's quite common for babies to be sleepy in the early weeks, but they tend to wake up after a bit. so maybe just keep an eye on things adn enjoy your sleep!
Doesn't matter how long she's feeding, they're all different on that score.