mom-babyblues2005, Hi and welcome to the Toilet Teaching board.
It does take time for a child to get to the point of going consistently on the potty. If she has recently started using the potty the time interval that she holds it can vary, as sometimes a child can hold it because they are scared. Honestly I would give it more time. On trips in the car you could place something in the bottom of the car seat in case there is an accident.
If you feel that she is doing it to take control, you can have her help clean up after any accident. Have her rinse out her clothes, put them in the washer/hamper/where ever you would like them to go, and then have dress herself. You may also want to give your DD something to work up to, such as a trip to the park or something she would like to go.
I hope that helps. Please keep us updated on your DD progress.