Please describe her behavior. Behavior is more important than poop or crop size to gauge her well being. If she is alert, bright-eyed, vocal, moving quickly when stimulated by external activity, shows eager interest in food, then she is going to be fine without an antibiotic.
If she is droopy, quiet, eyes dull and tired, uninterested in food, she needs the antibiotic since she probably has more going on than just weakness from hunger brought on by molt.