She's doing it because she can. She's getting some pay-off from it otherwise she'd quit doing it. And if you know that's what she's doing, why are you leaving her alone to do it only to come dance around about it?
Someone suggested a 2.5 year old may not need a nap and it's her way of telling you. I have a 2 year old (2 years and 3 months) and she still needs a nap. At nap time we sit down with her, and relax, and she goes to sleep. Although my 5 year old - when she was in daycare, she wouldn't sleep at the daycare provider. She wanted attention. We'd get her home and she wouldn't let us put her down. Once we got a sitter, she was able to relax and get the attention she needed and would take naps.
Putting on the diaper and/or sleeper backwards are both great ideas. Have her go potty before naptime, and incorporate that into some naptime routine. Kids LOVE routine. Even our 5 year old - our bedtime routine calls for us to go to their room at 8pm, read 2 books, use a flashlight to do "shadow puppets", and then time for night-night. At 8pm, she starts yawning and saying, "I'm sleepy". My thought - GOOD - the routine's working!!
I know my 5 year old likes me to stay in the room with her for a little while when she goes to bed at night. I figure it's a small price to pay for having her sleep comfortably. We'll work on that eventually, but for right now, it's a snall price to pay to make sure she's going to fall asleep and stay asleep. During the routine, I'm also sure to tell her, "You did a really good job today!" and tell her things that she did that were good - helping mommy, helping baby sister, etc., and that she's so smart, so pretty, and that I love her. She says thanks (unprovoked) for the praise and "I love you too Mommy."
Make everything a "go potty first" whether it's naptime, snacktime, tv time, or new activity time. Everything is "go potty first." Maybe even set the timer for every 30 minutes and when the buzzer goes off - time to go potty. (Our 5 year old still doesn't like to take the time to go potty, and we'll tell her "We're going to have to start setting the timer if you won't go potty like you're supposed to..." and she'll "straighten up.") When she potty's in the potty, give her LOTS of praise. "I really like it when you use the potty! That's such a good job!! You're a really big girl now!! That makes mommy very happy when you use the potty!!"
It's all about finding something that works for you guys. These are just some of the things we found that work for us.