。
She held the female office workers she'd been working with up until then in contempt.
Literal
She [topic-は] [up to that point-それまで] together work doing-came female-office-workers [object-を] held-in-contempt.
Several stylistic shifts give this version a casual or somewhat dated written register: いっしょに written in kana rather than 一緒に, 仕事して rather than 仕事をして (omitting the object-marker を, common in spoken/casual Japanese), 女事務員 with the older 女 (versus the more current/respectful 女性), and たち in kana for the plural marker rather than 達. These are the small register dials Japanese writers tweak to feel slightly more or less formal. Each individual choice is innocuous; the cumulative effect is a sentence with a more relaxed, vernacular feel. 軽蔑する ('despise, hold in contempt') is a strongly negative verb — heavier than 嫌う ('dislike') and more pointed than 見下す ('look down on').