Re-reading this thread... one thing I found out with my daughter (who is now 10 herself) is that she just doesn't wake up "naturally." That is, she will sleep much longer than she actually needs to unless I wake her up.
So the fact that she sleeps in doesn't really indicate much of anything, for her.
I've figured out how much sleep she needs by how hard it is to get her to sleep at night and how she functions during the day. She needs 8-9 hours of sleep. Less than 8 and she's moody and her brain doesn't function very well. Over 9 and she has a harder time getting to sleep that night. But if I let her, she will sleep 10+ hours (and then be draggy and never really sharp all day, and have a TERRIBLE time getting to sleep that night).
Anyway, that's just an addendum to what I said before.
Additionally, after I figured that out there was a transition period where she let go of her previous anxieties about getting to sleep (she knew she needed to get to sleep, she just was scared she wouldn't be able to and then things would be messed up the next day, etc). Once she reliably went to sleep (because of being really tired) a few times, she believed that she COULD, and relaxed, and getting to sleep became much easier in general.
Re: your daughter, kokobop, that sounds difficult. Is she anxious in general?