。
She belongs to the general affairs department.
Literal
She [topic-は] general-affairs-department [to-に] is-belonging.
所属している uses ~ている for an ongoing state of belonging or affiliation. 庶務課 (general affairs department) handles miscellaneous administrative tasks in a Japanese company — a catch-all department for office management, supplies, scheduling, and other support functions. This kind of organizational vocabulary (課 = section/department, 部 = division) is essential for understanding Japanese corporate structure.