Feminists

To win such a suit means that she would be acknowleged as the victim of a cad, resulting in less humiliation for her and more for him (not that it would be a major problem for him, but still) and this would help restore her prospects. Part of it depends on her social standing; it mattered more to the middle classes than to either upper or lower. And part depends on her age--older marriage was still acceptable and more common than it would be in the post-WWII era.

edited to add--Of course, the money itself would enhance her prospects; a woman with money was always more attractive than a woman without it.