Big hugs, Lauren. EWs are exhausting, especially when 2 LOs are tag teaming them! Do they wake each other? I know mine do.
As you know, my DS is very close in age to your DD and we recently gave up with the Gro-clock. Same as you, he ignored it and got up anyway if he woke before the sun, then on days he might have slept later, the light coming on woke him up and he would be grumpy. So we know don't use it and his wus range from 6-7.
I have kept BT consistent regardless at 7.15 to be asleep by 7.30, but if we were getting 5am wus I might go tempted to try later. I recently (in the summer) moved BT from 7 as DS started messing around loads at BT and taking ages to fall asleep. If your DD's BT has been the same for ages, maybe she is ready for a change too?
You could experiment for a week or 2 and see what happens? You could always move it back if you feel she's getting OT. Is your DD at pre-school yet? I find that has made a big difference in tiring DS out.