。
Tears ran down her cheeks.
Literal
Tears [subject-が] her [of-の] cheeks [object-を] tracing flowed-down.
伝う ('to follow along, trace, go along the edge of') is a specific verb for fluid running along a surface. 頬を伝って流れ落ちる ('flowing down tracing the cheeks') is the classic collocation for tears rolling down. 流れ落ちる is a compound: 流れる + 落ちる ('flow + fall').