I think at that time in England unlike in France (where dowry or dot had a more specific meaning), fortune or inheritance was the woman's dowry if she married, because until the Married Women's Property Act of 1882, the whole of her fortune became legally her husband's property, unless it was protected by marriage settlement. Her father had left it to her as her independent provision if she remain unmarried, but it would become her dowry if she married. Her guardian could not withhold it, but he could protect it by marriage settlement if she married properly instead of in an elopement without his knowledge. The marriage settlement could provide that the money was settled on her and her children so that she could have the income during her lifetime, or she and her husband could share the income during their lifetimes, and her children would inherit it after her death, or her husband could have a half-share of the income if he survived her, and her children could have it all after their parents' deaths, or if there were no children, that it could go to some relative or relatives of hers. In S&S, Mr Dashwood's first wife had money, and "the remaining moiety of his first wife's fortune was also secured to her child, and he had only a life interest in it."
Of course, a girl's brother or guardian could add to her fortune, but he was under no legal obligation to do so. That was in fact what Mr Dashwood had asked his son to do, since his son was so much richer, but John Dashwood was persuaded by his wife not to give a penny to his half-sisters.
Of course, a girl's brother or guardian could add to her fortune, but he was under no legal obligation to do so. That was in fact what Mr Dashwood had asked his son to do, since his son was so much richer, but John Dashwood was persuaded by his wife not to give a penny to his half-sisters.