。
She always teased me when we were working together.
Literal
She [topic-は] we [subject-が] together work do [time-時] always me [object-を] teased.
Inside the temporal subordinate clause 我々が一緒に仕事をしている時 ('when we were working together'), the subject is marked with が rather than は — Japanese reserves は for matrix-clause topic, so embedded clauses default to が. The 時 ('time') turns the whole clause into 'at the time when ~,' a temporal background for the main verb. The main clause 私をからかった has the speaker as object: she was teasing me. The verb からかう covers everything from playful joshing to unwelcome ribbing, and こうしてからかう relationships are common between coworkers and classmates.