Ista was visibly perkier in the few hours of receiving fluids between when I dropped her off and when Mark and I picked her up to go down to the emergency vet. Also the wash of barium had moved the obstruction along somewhat. They are keeping an eye on her with X-rays and noting whether the obstruction continues to move or whether it sticks put somewhere. There is some chance she will pass it and will not have to have an operation after all. We are hoping.
It's going to be a quiet night around here, but things are going as well as they could under the circumstances.
I am exhausted. I do appreciate the individual well-wishes in comments, but I'm not going to have the energy to respond to each in turn.