My kids were never great nappers but they slept all night from the time they were infants.
I just never tried to force the sleeping thing, but I made them lay down at the same time each day.
There are times when it would be better if they actually slept, but you really can't force a little kid to go to sleep for a nap.
Some days, rest time is all you can ask for and if they are in the habit of it and do it, that's a great thing.
My kids didn't sleep but they would lay still and quietly and in that regard they did at least get some quiet rest time.
Sometimes they would konk out, but rarely.
And I never resorted to the car thing. I know it works for some people but the more you focus on the nap thing, the more they fight it, in my opinion.
I told my kids they didn't have to sleep, but they had to lay down. They did so pretty willingly because I never used the "n" word...nap.
Try using a different tactic and if she doesn't actually fall asleep, don't worry so much about it. As long as she lays down.