。
She married Tom last month.
Literal
She [topic-は] last-month Tom [with-と] married.
結婚する takes と (the partner is whom you marry 'with'), echoing how Japanese conceives marriage as a mutual joining rather than an act with an object. 先月 fits a tidy set of relative time words — 今月 (this month), 来月 (next month), 先月 (last month) — and note the irregular reading: 先 reads せん here rather than the usual さき.