A slow heart rate is not anaphylaxis unless it progresses so much that death is imminent. I doubt we will work out what happened on this thread but I dont think it was an allergy
I would reinforce what others have said - this is a common situation where a consultant microbiologist, provided with samples and blood, will be able to advise on a suitable antibiotic regimen. Nobody here can help you even if they are themselves a microbiologist as they wont have the laboratory data. You can always ask to meet the microbiologist - many of them are delighted to come to the bedside and discuss.
I would also add what I commonly write here - anyone who says they are the best or the case is the worst needs to be taken with a pinch of salt. Pus in the abdomen is quite common with appendicitis and if your daughter is young and fit, and stable after a day or so the outlook is hopefully not too bad.
Best of luck