could it be the new found freedom of her controlling when she is in or out of bed.
i found DD1 did this for a few weeks once she learnt she could conrtoll in and out and thought 4 am was a great time to play.

also we have changed DD1's doiet as we found some foods and lots of gluten at night made for a horrible nights sleep, unsure if it upset her tummy or what but minimal gluten and sugars and she is alot better