I know it's tempting to let them cry and see if they miraculously fall asleep on their own! But I'd caution you against that... She's been sleeping so well at night, I'd hate for her to start being uncomfortable in the crib or have issues because she was left to cry.
I'm no nap expert (quite the contrary! :? ), but from what I've seen successful with others, you might want to try putting her down a bit sooner. Maybe waiting until she rubs her eyes is too late? If she usually goes down around 1.5 hrs after awakening, maybe start a short routine ending just before that (book, song...).
It could also be something developmental...learning new skills like rolling, sitting up...they seem to like to practice them at nap time! :roll: