I have gone with my broad range of 5 kids (5y-18y last trip) as a single parent several times, and last trip my DS 15yo acted as the other parent for a parent swap. He would go through the ride (either alone or with "extra kid" (9yo DS) that wants to ride) while I waited with the non-rider (5yo DS). When he finished he would wait with the non-riding child (5yo DS) that did not go while I got a chance to ride.
The first person riding has to wait in the line unless you have fast passes, but usually they allow the waiting "parent" to go through the single rider or fast pass line. Also at several of the rides they allow you to take the "extra" kid (9yo DS) back through the line again.
We found that on rides the two younger boys did not want to ride we would use the single rider line if it was available. We would just have to go separately, but it worked out.
I do not know if you are comfortable having your 12yo wait with your 8yo, but they can usually stand near the attendant while you ride. It used to be that the child swap happened when you got on the ride, but now it happens at the entrance to the line.
I am now going with a 2yo DS, so we will be parent swapping a lot or I will just not ride.
I think EE would be a good beginning thrill ride for her, but I would definitely do it during the day. Also, ToT in the day as it freaks me out a little a night still. On SM, I sat behind my 5yo and kept my hands on his shoulders the whole time and he did great and was eager to do it again. I had to stretch to reach him, but I did.