Once you have a diagnosis you'll be able to google it and find tons of resource.
BUT each child is different. For example, one of the things that was suggested to us to help kiddo get centered and more focused was bouncing on a mini trampoline. NOOOOOOOO!!! That wound kiddo up like a watch that winds as it is moved! We got rid of that after a couple of days.
Rocking, did a good job, we put a smaller adult rocking recliner in his room. Either he would go sit, watch TV and rock or we could sit, hold him in our lap, and rock him. This one was a good thing.
A weighted vest, did a great job for a while but Head Start messed this up. They were supposed to put a backpack on him with a couple of books in it when he was going to do work at the table.
Come to find out they were putting a LOT of books in it, basically punishing him, when they just wanted him to sit down and shut up. We found this out when we got a note that child welfare had interviewed him during the day at Head Start.
The worker was a friend of ours and told us they had a complaint the teachers were being mean to my kiddo. The teachers weren't there much longer.
By making the weighted item a punishment they took any sort of benefit we were getting from it.
So, even though an option is suggested it might not be "the one" that helps your kiddo best. Find what works for her.
To be honest, in your situation there would be no way I'd be letting a 4 year old do this stuff. I would dress them in an outfit they couldn't get out of and I'd fasten them in their car seat and that would be that. No way they'd be the boss of what was going on in the car. They aren't old enough or mature enough to make those choices.
You are the parent, fasten her in and go. If she cries...well, she cries. Car seat safety is not an option.