。
She has been unable to speak since birth.
Literal
She [topic-は] born time [since-から] speech [subject-が] unable.
口が利けない means 'cannot speak' — 口を利く (くちをきく) means 'to speak/talk,' and the potential negative 利けない means 'unable to.' This is a somewhat older or literary phrasing; modern Japanese would more commonly say 話せない. 生まれた時から marks the lifelong duration.