She was a lawyer, but then she changed track completely and became a doctor.

track 的本义是"轨道、跑道"，引申为"路线、路径"。 在职业发展语境中，track 常用来比喻"职业道路"或"发展方向"。 changed track 这个短语表示"改变轨道/路线"，引申为"转变职业方向"。