How to keep her in her car seat?

This is a really tough problem!! It could be a matter of life and death. My sister used big diaper pins above the latch and the chest clip to pin the straps together. This made it harder for my niece to unbuckle the car seat. You also have to be VERY strict about this and make sure she knows she will be in big trouble if she gets out of her seat. If you make it very clear she HAS to stay in her seat she should stop climbing out. Good luck.