Why would Louise feel she would be free to do nothing all the rest of her days?

Louise Mallard is looking forward to a very specific type of freedom: freedom from what was, apparently, an unwanted marriage. Although her husband "never looked save with love upon her," she sees "a long procession of years to come that would belong to her absolutely." Without a husband, Louise will be her own master; she will not have to compromise or obey anyone else's demands on her. To this end, she thinks,

There would be no one to live for during those coming years; she would live for herself. There would be no powerful will bending hers in that blind persistence with which men and women believe they have a right to impose a private will upon a fellow-creature.

Louise will be in charge of her own life, and she will not have to submit her wishes for someone else's approval. Her days will belong to her. Therefore, she believes she will be free. She wouldn't necessarily have to work. Chances are, if she felt somehow obligated to enter into a marriage that she didn't particularly want, she is likely of a certain social class: she is not poor. Further, Louise would benefit from inheriting everything that belonged to her husband, likely preventing a need for gainful employment. However, even if she does have to work, that does nothing to alter her freedom from a marriage that seems to have produced the "lines [that] bespoke repression" in her face.