hi,
your lo is likely still too small for a 4-hour EASY, but i think you can start to play with her awake times a bit.
maybe instead of an hour, try extending her for an hour & fifteen minutes for a few days. then try adding a little more. it kinda sounds like your in a bit of a cycle - she's only awake for a little while, so she's only a little tired, so she only sleeps for a little while - and so on.
that 3-5 month age range is a delicate line between A time and overtired, but it is when things really start to extend.
good luck!