Do you want her to keep a nap? It sounds like she is sleeping around 12 hours at night, which is typical for that age, isn't it? Have you tried waking her up earlier, say around 8 AM, and then doing the nap around noon? I had to move my twins' afternoon naps earlier as they got older so that they didn't stay up too late, but couldn't just drop it as they became really cranky without a nap. They dropped their naps at almost 2 1/2, and for a while after that would fall asleep every time they were in a car.
