Oh honey, if she dropped all the way to 60% with a low blood pressure she's most likely septic and has multiple systems involved. A PO antibiotic an hour or two earlier was not going to change it, maybe a day before. Could you have called the doctor with the result, yes, could you have checked her sat when you have her the med, yes. Would it likely have changed her going to the hospital no, at least when you sent her in they knew why. Live and learn.