Kate Chopin decided to introduce the protagonist as Mrs. Mallard rather than by her first name because she is an unhappy woman who is trapped in her marriage. She cannot set herself free and endures it until she receives the news that her husband has died in a train crash.
Initially she feels grief, followed by thoughts of freedom and years of happiness for herself, until her husband shows up and causes her a heart attack. In the end, she dies and we learn her first name: Louis.