I think you're having the classing 10 hour OT wakings. They happened at our house for awhile too. I don't know if your DD is teething, but for my son whenever he gets teeth in it makes him EXTRA tired, so it meant I had to put him down 30 minutes earlier for both nap and bed.
Everyone has given great advice, so I'll just be sure to check back in a few days to see if you're having any success.
One last question -- have you tried any sleep extention methods at that 4:30 waking? In other words, have you tried giving warm milk, rocking, soothing, ANYTHING to help her go back to sleep?