Tough situation TL. This would call for an Infectious Disease sub-specialist to sort through the available alternates, depending on the organisms involved, and the clinical situation. Not really able to get more specific in a web forum. If you are in a place without such folks, no doubt a tele-consultation could be arranged.
I seem to recall that allergy to Vanco is uncommon, but with what you describe, I doubt anyone would persist trying that one. Going slower wouldn't work.
Best wishes for your daughter. It's another of many reminders that appendicitis in adults, especially women, is not to be trifled with.