* The societal expectations of the time: The story was written in 1894, and the expectations placed upon women during that era were incredibly restrictive. Marriage was seen as a woman's primary purpose, and the idea of a woman finding happiness and fulfillment outside of that role was often seen as scandalous and even dangerous.
* The institution of marriage itself: While not explicitly stated, the story heavily implies that Louise's marriage wasn't fulfilling. She was trapped in a relationship that likely stifled her individuality and desire for personal expression.
So, while there isn't a single antagonist character, the societal pressures and the limitations imposed by her marriage act as the primary forces preventing Louise from achieving true freedom and happiness.