The diagnosis is that she's been too active and this is slowing the healing. A sort of blood blister has formed at the surgery site, and that is the source of the blood that seeped out of the incision. The vet hoped that she would spend the weekend sitting in her crate (probably in the litter box), not moving around, and hopefully letting this start to heal. if necessary, they would put in a drain.
I'll call tomorrow and see how she's doing. I could crate her here, though we'd probably have some Issues: the crate that has become a permanent fixture in my study most definitely belongs to Fish.
And I leave next Sunday for Denver: non-optional work trip. Here's hoping she's substantially improved by then.