。
She held her own working alongside the men.
Literal
She [topic-は] men [with-に] ranking-with-and worked.
伍する is a literary / formal verb ('to rank with, to be on a par with'), built from the kanji 伍 (one of an old set of five — '伍' was historically a unit of soldiers) + する. に marks the group one ranks among. The te-form 伍して acts as an adverbial phrase modifying 働いた — 'worked, doing so on equal terms with the men.' This kind of lexical choice nudges the sentence toward a written register; 男たちに混じって or 男たちと一緒に would be more colloquial.