Answer and Explanation:
First, let's define self-assertion as a person's ability to express themselves confidently, inspiring respect in others. Louise Mallard, the main character in Kate Chopin's "The Story of an Hour", did not seem to possess self-assertion as a personality trait at all. Maybe she was merely seen as fragile by the other characters, due to her heart condition. Maybe she had been subservient to her husband and others all her life.
The way the other characters treat her make it clear they do not see her as a strong, opinionated woman. At the beginning, her sister and a friend carefully break the news that Mrs. Mallard's husband had died. So far, the way they treat her is understandable. Her heart is fragile, so they are afraid of shocking her to death. However, Louise asks to be left alone when she goes upstairs, to her room. She wishes to be by herself. Her sister, nonetheless, is incapable of respecting her wish:
"Louise, open the door! I beg; open the door--you will make yourself ill. What are you doing, Louise? For heaven's sake open the door."
This shows that Mrs. Mallard wasn't able to assert herself. Her will was not respected. Instead of leaving her alone, her sister came to bother her, afraid that she would be in such a state of fragility that she would get sick.
However, it was right before her sister came to her door that Mrs. Mallard realized she does have self-assertion. It had been hidden somewhere, but she has it. She answers her sister in a commanding tone:
"Go away. I am not making myself ill." No; she was drinking in a very elixir of life through that open window.