I would say the correct answer is to foreshadow the ending and make it believable.
If you think about the ending, this option will become clear. Mrs. Mallard died because of heart failure, due to 'joy that kills.' She heard that her husband died, and started feeling happy about her newfound freedom - but it turned out he was actually alive and well, and this is the reason she died - having her freedom suddenly taken away from her. To know that she initially had heart problems only helps us believe that she actually died of happiness/sadness.