I was also going to suggest a crate. Get her used to it in the house, pop her in, cover her up & start off with small journeys. I have just bought one for Tilly, not for the same reason though. She loves the car, but won't sit still. She is also destructive in the car. The other week I visited our local GSD rescue with a cheque from our training club. The lady from the rescue had come to the car to say hello to both the dogs. Afterwards, I was only standing 10 feet away from the car & Tilly shredded a whole pack of poo bags in the back, just because she wanted to be the centre of attention, as usual. Thats put a stop to her little exploits