Back with a happy ending!
In 3 hours at the E-vet little M got better care than in 3 days at Banfield. Banfield was content to send her home yesterday with "we don't know what else to do other than send you out of town for an ultrasound" - omitting that a local vet does ultrasounds. She spent all day in their care yet she was discharged with very dry very pale gums - obviously still dehydrated.
E-vet administered IV fluid containing sucrose (?) to help give her blood some viscosity, gave subQ fluids, gave a Cerenia injection to calm the bowels, and gave a pepcid injection.
She said nothing -food-medicine-water was to be given by mouth until 24 hours after vomiting had stopped (contrary to Banfield's order).
By this morning little M had perked up, by lunchtime she was even better. We just got back from another visit to the E-vet for another round of IV fluids. tomorrow the catheter can come out and she can try to eat again.
Thank you all for your prayers, and Dr Feeman, thank you so much for your advice.