I think at first and each bay is different what´s important is the order of EASY not so much the 3 hour mark, i would feed my baby and start taking clothing off if he fell asleep before he was dome eating to make sure he was full, babies this age don´t get a lot of A time just looking around is activity to them try to keep her up after a feeding even for 5 min, tickle her feet gently talk to her, and then you can let he go back to sleep, maybe she will need this to be 2 hour easy until she can pull the 3 hour stretch mark, during the day if she sleeps more that the 3 hour, wake her and feed her, at night of course let her sleep,
hope this helps best of luck