Yes, there has been progress!
Day 1
Our first night consisted of us going out into the garage with the door shut and she was off leash. I opened the back door and put treats on the door threshold (the bottom part of the door). She was cautious, but would slowly walk to the car and eat the treats. I calmly praised her as I stood a few feet away. I didn't want to scare her or make her think I was going to force her into the evil backseat.

I gradually put the treats further into the car, but when they got past to where she could get them with all 4 paws on the ground she looked at me, whined, and walked away. I pulled them closer and encouraged her to try it again.
Day 2
On our second night (last night) we did the same thing, except this time she was much more comfortable with getting them off the threshold so I started to put them out of reach. She used 1 paw to elevate herself so she could get the treat. I said "jackpot" and tossed a few more treats on the ground. After about 10 minutes she had both paws on the car and was reaching in the back seat to get the treats.
She is definitely making progress, and as stated before, counter conditioning isn't very glamorous, but it's necessary.
I'll keep you guys posted!