Unfortunately small babies sleep quite light. It has to do with their maturing neurological system. They are bombarded with millions of information every day, building synapses all day and processing all that information during the night. They dream quite a lot and they drift on and out of sleep all night.
Sth that you can try is to keep more interacting with her during the morning rather than afternoon? and have more relaxing activities for her at afternoons?
They usually start sleeping better and deeper later when their neurological system is more mature too. Until then I suppose we have to just live with 3 h sleep per night lol...