Sorry to note that you are having a difficult time.
Rashes and diarrhea
in children due to infection is not unusual and very often blamed on 'antibiotic allergy'. It is important that serial stool and blood cultures are done AGAIN to exclude another infection, 2D-ECHO to ensure the heart is ok and ensure absolute lymphocyte count
returns to normal once she is better.
I hope she is still under specialist care until all the above has been sorted.