How old do you have to be to be in the single rider line?? We'd risk it if hubby went 1st, then dd (will be almost 9 on our trip) and then me... so he could fetch her when she disembarks, and I would be right behind... plus odds would be she'd end up riding with one of us anyway??
You already mentioned that she won't do it, but as another person said, 7 is how old you can be to ride alone.
DS and I used the SR line, and it was fabulous! He's 8, and had just had the experience of being on an airplane one row away from me, and now he wants to fly like that all the time. So being in a car that's so much like Test Track (he's been on it) without me was a breeze for him!
We were in different cars; different ride cycles, actually. Nice thing was that we'd waited with a family of 4 with 2 being grown children, and after a ride stop that added about 20 minutes to our 40 minutes estimated wait time (which started BEFORE the sign, so it was longer), we were all on friendly terms. I was in the ride vehicle with one of them, he was in a ride vehicle with two of them, so it was like he had friends with him.
He had a GRAND time, and it didn't reduce our enjoyment AT ALL to ride 30 seconds apart! We had a place to meet set up, which then became "if you want to dawdle along and see the sites in the exit area, go for it, but once you completely exit don't go beyond Stanley...but don't get in peoples' way if they want pictures of Stanley, either". What can I say, it was quite a line! I had time to modify the instructions, LOL. But as it was, we ended up exiting at the same time (now that I think about it, his car was probably racing the other car that left with mine) and it was simple!