THIS IS NOT CIO!!!!!
YOU ARE NOT BETRAYING YOUR LITTLE ONE!!!!!
Imagine...you take her out for just a second, and diaster hits. She will not remember this, but who could forget if she is left crippled, scarred or worse?
In the meantime, I would make it a point to take her out on a regular basis, when you are not on a time schedule or the freeway. As soon as she starts crying , pull over, remove her from the seat, and comfort her, making sure to explain why it is necessary. This is what I did with mine, and now, she mostly just snoozes or plays. In fact, we had to make a 2 hour each way trip, and she slept the FULL TIME both ways. I believe that by setting up a situation where I responded to her cries, I was building up her trust in the fact that she was not being stranded.
You are a wonderful, loving mom...and do not allow this experience to make you feel badly about yourself.
Also...I never did it, but maybe she will be comforted by having a pacifier to use only while in the carseat. I do always give her a small toyto play with, however.
Does she have a favorite lullabye tape? That really helps my little one. But ultimately, I think that she does well because of my repeatedly stopping to comfort her.