Have you thought about trying to find a rear view mirror to attach to her helmet? I usually end up driving from the DC area to Louisiana to visit family with just me, my 20 month old son, and my puppy dog. It's amazing how much having a little mirror at that age will distract them. My son is also going through an anti-carseat stage and I've found that handing him a mirror will distract him enough for me to get him buckled in and then he usually forgets he's in his carseat for an hour or so.
We just got our trailer today, and I think I'm going to see if letting him wear his helmet around the house works. He also loves to do things in front of a mirror, so I might also try to get him used to putting on his helmet in front of the mirror when we're getting ready.