。
She always complains about her teacher.
Literal
She [topic-は] teacher [about-について] always complaints [object-を] says.
不平を言う means 'to complain' — literally 'to say complaints.' 不平 (ふへい) means 'dissatisfaction' or 'grievance.' A common synonym is 文句を言う (もんくをいう). The いつも ('always') combined with the habitual present tense 言う emphasizes this as a chronic behavioral pattern. The particle について marks the teacher as the topic of her complaints.