。
She has been working at a publishing company for two years.
Literal
She [topic-は] publishing-company [at-に] two-years is-working.
The duration expression ２年 comes between the location and the verb, modifying 勤めている to express 'has been working for two years.' No particle is needed on the duration — Japanese typically places bare time-duration expressions directly before the verb. 出版社 (publisher/publishing company) uses the suffix ~社, common for company names and types: 新聞社 (newspaper company), 商社 (trading company).