。
Poverty doesn't suit her temperament.
Literal
Poverty [topic-は] her nature [with-に] does-not-match.
性に合う/合わない means 'to suit/not suit one's nature or temperament.' 性 (しょう) here means 'inborn disposition' rather than 'sex/gender.' A statement about someone's personality — she is not the type to tolerate being poor.