My 7 year old falls asleep straight away at bedtime, which is any time between 7 & 8 pm, but then wakes any time from as early as midnight onwards, then cant go back to sleep ?
There are a number of options you could try, I'm sure you must have tried some of these already but here goes:
Extend the bedtime to 9 p.m.
Ensure that she has some physical activity in the evening i.e. tire her out a bit.
Does she nap in the afternoon? If so then perhaps reduce the amount of nap time or stop it all together depending on what she's comfortable with.
Environmental factors: Is it something in the room that's bothering her? Try changing things up a bit.. different pillows/bed position/night light/comforter/room temperature etc. Try letting her sleep in a different room or a night or two.
Lastly if this is a recent occurrence there could be something bothering her which causes her to stay awake. Probe a bit and see if there is something you can help with? A class at school which she dreads, an after school activity she is not looking forward to (if this happens only on some days of the week).