If she ate the potpourri - I hope your vet consulted with a poison specialist - do you know if that occurred? Bc, there are all sorts of chemicals on potpourri. When the body continues to vomit (and nothing is directly stimulating the gag), it tells me it's trying to desperately get rid of something - so either the vet missed something on xray, or, there is a toxin present. What did poison control say?
I'm so sorry that she is suffering, and you as well - this must be very scary for you.