Again. She completed the purchase, it was her property, she accepted the bag and walked some distance knowing it was not properly bagged and did nothing to resolve it.
Your what if scenario is not analogous.
It is the baggers job to bag it properly, not hers.
If I pay someone to balance my tires I expect them to be balanced, if on the way home I feel a sudden resonance at 70 MPH and a wheel falls off is it my fault for not double checking the tire technicians work?
It happened on their property and was caused by someone not doing their job.