Has she always been hard to get up, or is this a new thing? If it's new, it may be stress, and you need to find out what is bothering her.
I agree that it could be too much sleep. Try waking her up a little earlier or having her go to bed later and see if that helps.
Definitely establish a routine in the evening and morning. Maybe buy her a cute alarm clock, teach her how to turn it on and off. Put it on the other side of the room from her bed, so she has to get out of bed to turn it off.
Give her something to look forward to in the morning that she can have if she gets up willingly. Maybe let her choose her own breakfast cereal, buy her a couple of new school outfits, or let her do something fun in the morning, like read aloud to her, let her spend a short time doing a computer game, etc.
When you say you've tried rewards, how long have you tried them. You need to try it for a long enough time to see if it works, several days at least. I would also add a negative if she doesn't get up. Just make sure it is something you are willing to enforce.
One thing I do with my girls, if they don't get up or are running late, I make them get up 15 minutes earlier the next morning. They will eventually get the picture that if they get them selves up and get ready on time, they can sleep longer.
I have an 18 year old that is still hard to get up, but she finally learned, because I didn't wake her up a few mornings and she had to pay the consequences of being late to work. Now she rarely has to be told to get up.