Hi C.~
You know the saying 'if it isn't broken, don't fix it.'?
...Okay, Im just kidding, but what a problem to have! :) I think the answer might just be routine. If you are sure she is going to bed early enough, maybe you could turn 'sleeping in' into its own reward. Perhaps put together some sort of predictable routine with your daughter, that on some days she has to get up by...(whatever time)...and then on other days she can sleep until...(whatever time)... Maybe even throwing in an incentive, like sleeping in as late as she wants on the weeknds if she gets up on time the rest of the week?! Personally, I would just adjust my days the best I could and worry about school later. Im sure she will go through many sleeping changes by the time you have to worry about school, and by then she'll have much more ability to understand being on time.
Good luck with your sleepyhead!
~L.