I just want to chime in that daylight savings is just around the corner. I find my son wakes up earlier this time of year, I think it is due to it being lighter earlier.
Also, if you would like to preserve your existing routine, why not shorten her nap? It will probably help when she goes to school anyway. (as will an earlier wake up time) I know you mention that she is getting a shorter nap right now, but she is bound to get so tired that she will occasionally try for a longer nap in the next few days.
Have you checked to see if her 5 year molars are coming in? That might explain why she needs sleep but isn't getting it.
Adjustment periods are tough, but once you figure out how much her new total sleep amount is (for the day), you can adjust her bedtime so that her wake up time is when you hope for it to be.