L.
It sounds to me like this is not so much about the car seat, but a control issue and power struggle. She could pull the same behavior over bedtimes, which clothing to wear, what she want's to eat. She need's to recognize that you are the authority and she must obey. How do you get her to obey in other areas?Unfortunately, car safety is not an area you can compromise in order to get her to obey. The screaming is really just a temper tantrum and is unacceptable. You need to play mean mommy and tell her this is the way it is, like it or not, and she must obey you and not carry on when she doesn't get her way, and if she continues with the screaming and carrying on, it's time for a punishemnt.