Grace, there is no question that raising your own kids is harder than anything else you might attempt.
Your daughter sounds a lot like I was at that age. When I was about 5 or 6 my dad had a talk with me about staying up late. He explained that people need 8 hours of sleep, and due to the way the rest of the world was arranged, this would require that I go to sleep at a certain hour.
I still read in bed using the hall light, but I tried to be more careful about not letting anyone see me being crabby the next day.
With my kids, my inclination would be to let them stay up as late as they like as long as they are in their rooms, quiet, AND are able to get themselves up in the morning and get where they need to be. The Muffin Man is a bit more inclined to have everyone on a schedule, but the only time we've really enforced bedtime in the past couple of years is when they miss the bus and have to be driven to school. Once wasn't a problem, but two mornings in a row would get them a fixed bedtime for a week. They seemed to learn pretty quickly. In general, I'd rather they were honest about being awake than sneaking around in the dark.
There are no simple answers that work for everyone. You have my sympathy and best wishes as you try to work through this with your family.