E.M.
Sometimes they change their sleeping pattern for no reason at all. Or it could be a growth spurt. Maybe this is her new sleeping schedule that she has set herself? I'm all about child-lead parenting... sleep when baby is sleepy, eat when baby is hungry type of thing. So I'm very happy to hear that you don't mind getting up with her. My advice is to follow her cues, make sure she isn't getting too over stimulated during the day, and when you notice she's getting drowsy you can put her to bed/nap (where ever she sleeps).