This can be so hard at this age. My son was ok in the car for the first bit, but would freak out if the car ride was any longer than 30 min. I would talk to him while I was driving ,put music on, and when stopped at a red light or something, I would reach back and reassure him that I was there for him. It's tough.
I have to say though - that having someone ride in the back seat with the baby...was never a good option for my husband and I. He would cry even more because when he saw us sitting with him he wanted us to pick him up...which obviously is NOT an option while you are driving in the car. I found that he got used to it over time...not fun to hear him cry...I felt awful! But the carseat is a non-negotiable obviously. Also getting into the habit of this can also cause "accidental parenting", we have friends who did this, and their son is almost 18 months old, and they STILL have to do this. I personally think they have caused more work for themselves in the long run. (Just my honest opinion) Your daughter might be different with regards to that! I think once in a while is totally fine though.
Once my son was forward facing it was a whole other story.
One thing I tried when he was rear facing, was I put a little mirror on the seat facing him...so that he could see himself, and me! He loved that!!! Just a thought!