I am assuming that because she is getting up so early that she is tired during school and that is causing problems?
Or is the problem that you need her to be sleeping longer so you can get things done?
Some kids just don't need as much sleep as other kids do. If her sleeping habits aren't causing behavioural or physical problems, maybe she is one of those kids, and you just have to get used to it.
If it causing problems like irritability or lack of concentration, then there are some things you can try.
Limit sweet or starchy or large snacks before bedtime. No exciting movies or physical activities just before bed. Try to keep to a schedule.
You didn't mention naps. Does she take them? If so, cut back. If not, you might try having her take a short nap during the day, and putting her to bed an hour or so later than her usual bedtime.
If having to go to the bathroom is waking her up, don't let her drink anything before bedtime. You might try waking her up after a few hours in bed and having her go. Maybe she will fall back to sleep and not wake up again. But she might not go back to sleep again for a while, so it might not help.
Doe she wake up early all year long, or just when it starts getting light earlier? My kids wake up earlier during the summer because the light wakes them up. They sleep later during the winter. You can intall room darkening blinds.
Once she starts being in school all day, she might be more tired and sleep longer anyway. If she is crabby when she gets home have her take some quiet time for a short while.
Hope this helps.