Thanks for the input. They did take an x-ray but it didn't reveal anything. The vet didn't want to do an ultrasound until she was stable, by which time it was too late
The problem with these situations (and don't take this as blame, it isn't) people tend to wait until the situation is dire. Generally, by the time the vet gets their hands on the animal they can't risk surgery (with a temperature of 90, it sounded serious!)
So don't feel bad. The vet did the right thing (as did you). The chances that she would have survived an immediate exploratory are slim. Possibly after initial stabilization it may have worked out, but that's a judgment call that's high risk.
My one question is did they do any x-rays? With internal bleeding, I'd think they would have considered it.