why does dd nap when we have to leave??

always
I have to pick my oldest DD up from school because we dont get a bus and Brianna always falls asleep like a half hour before we have to go and then that is her ONLY nap

it is so frustrating because now its gonna be a fight to keep her up until at least 8 oclock and if I cant she will take another short nap and then be up until after midnight

thanks I needed to vent