Baby Houdini

I decided to take emie to a trip to meijers to get more cloth diapers. Yes we are transitioning from disposable to cloth. I tried cloth last week and loved it. I haven't gotten any poop diapers on cloth yet but i think in the long run switching is better for emie since she always has diaper rash and rashes no matter what brand of diaper I use. While driving to Meijers she decides to take her arms out of the car seat. It's not the first she has done it, so I loosened the belt around the arms just a little thinking maybe it was too tight. Didn't matter even when being looser she still got out of it. Any suggestions on how to get her to not get out of it? i was thinking of putting the lap belt around her besides the car seat belt she has on her. Not sure what to do yet....