My DD started doing this a few weeks back, wanted to sleep until 10:30-11:30 in the morning but then she wanted to stay up until midnight. I now wake her around 7:30 in the morning if she isn't up already and she goes to bed at 7:30 at night. She doesn't sleep for this long, never has though, she's always been a terrible sleeper. She usually has a feed in the early hours of the morning. I wouldn't wake her, sounds like she needs that extra sleep, it's not like it's affecting what time she goes to bed. Possibly a growth spurt. Well done baby girl on being such a great sleeper