The Increadible Shrinking Bedtime

I have been trying to find a happy medium with Abby. She usually gets up around 8 am. If she takes a nap, it's usually 2-3 hours in the afternoon. She can't sleep again until around 10 or so. I have tried putting her in a dark room and just leaving her there. She will cry or scream or play or get up and come out until around 10 o'clock and then drop off. It's tough. During the summer, we tried no nap. She would hit the hay around 7 pm. Now she can't make it that long anymore. I'm not sure if it's because there isn't the excitement here in Montana that there was with her cousins around or what but she will sleep whether I like it or not around 12 or 12:30 after her lunch and stay that way until around 3. She is going to be about 8 pm and actually going to sleep. We have had so many different routines that it's hard for me to determine what is the best. Anyone else have trouble with their kids sleep patterns? Does anyone have suggestions?