It is a developmental shift, she is growing & changing.
Try putting her down at 1:30 or 2:30.
When I changed my daughters nap time it helped. She was not ready at the earlier time any more & wouldn't go down before two, but then by 4:30 5:00 she was crashing at the table in her food if she did not nap. I started laying with her around 2:30 & she would drift off & usually sleep for 60 - 90 minutes.
She ended up giving up naps around age two. It sucked.
Just before she turned 3, I started driving to get her brother at 2:30 & she would fall asleep in the car. I found I could not get her to the bed & keep her asleep, but she would "rest" (usually sleep) for an hour or two on the couch.
We did that for almost 5 months, I am sad to say, no more nappies at all. I put them both to bed at 7:15 & she sleeps later than my son.
Experiment.
You will find the right combination for your family. Pay close attention to her "tired signals". I found if mine were overtired, I could forget getting them to rest.
P