One can only make assumptions regarding the fact that Mrs. Louise Mallard is referred to as Mrs. Mallard, instead of Louise, throughout Kate Chopin's short story The Story of an Hour.
1. Mrs. Mallard has been oppressed and controlled by her husband Mr. Brently Mallard over the course of their marriage. Therefore, her identity is that of Mrs. Mallard, not of Louise.
2. Given that Mrs. Mallard is a married woman, she is simply referred to by her married name.
3. Kate Chopin may want readers to see Mrs. Mallard as a mature woman and not a young woman (in order to compound her pre-mature aging--given that she "was young, with a fair, calm face," but her face had lines which "bespoke repression."