When we did it (not in a wheelchair, but my sister was in a boot and couldn't stand for the show), we got a FastPass in the morning, and when we got to the show, we asked them where the wheelchair section was and they told us where to go. There were (I believe) 4 benches in our section (behind a railing), and almost everyone who was in a wheelchair or ECV got out of their chairs and sat on the benches, so they didn't allow anyone who could stand to sit (I ended up sitting on the ground between my sister's feet and the feet of a very nice older gentleman - I don't think I was supposed to, but nobody stopped me).
If it's not crowded there may be enough room for you and the girls to sit with her, but if it is crowded, CMs will be very insistent that you stand (or at least they were very insistent when I was there).
I thought the view from our section (I believe we were in yellow) was pretty decent - and I was sitting on the ground.
As the PP said - ask if you have any questions, the CMs were very helpful.