。
She climbed down off the roof.
Literal
She [topic-は] roof [from-から] descended.
下りる is the intransitive 'go down' — the descent happens to the subject — paired with the transitive 下ろす ('to lower/take down'). For a roof, 下りる is the natural choice: she's the one moving, not something being lowered. The starting-point particle から marks the source of the motion; the destination would be marked by に or へ if mentioned, but here only the origin matters. Note that 下りる shares the same kanji as 降りる, which is preferred for getting off vehicles (電車を降りる) — both readings are おりる, and modern usage is somewhat fluid, but 下 leans toward going down from a height.