Her brain is going through huge spurts of development and she is sooo busy its harder for her to settle down. This doesn't mean she should give up naps, especially since she still acts like she needs them.
Make it "quiet time" instead of nap time. If she watches t.v. at all, it shouldn't be within an hour of when you want her to go down (t.v. actually wires kids brains making it harder for them to fall asleep). Also try to not have any outings or other activities that will get her excited in the 30 minutes or so before her nap.
Get her room as dark as you can, close the blinds/drapes and turn off the lights. You can play some quiet, relaxing music if it doesn't keep her up. Give her 1 or 2 small toys or stuffed animals she can play with in her bed. For a while at least, you may have to lie down in the room with her - just make it a household quiet time. (I had completely thought my son had outgrown naps by 3, but when he went to a new daycare who had a quiet time like this everyday for the whole class, he started napping again! and was a lot happier in the evening too).
You'll probably find that she goes through several more phases like this in the next few year. She's just trying to do and see everything and to adjust to all the growth her brain is going through (which also makes it more important for her to have quiet rest time).