。
She left here right away.
Literal
She [topic-は] right-away here [from-を] departed.
立ち去る is a compound verb: 立つ ('stand') + 去る ('leave / go away'). The 立ち is the i-stem of 立つ — combined, the compound captures the act of rising and leaving in one motion, often suggesting an unceremonious or decisive departure. を with motion verbs marks the place departed from, not an object affected (Xを出る 'leave X', Xを通る 'pass through X', Xを立ち去る 'depart from X'). The departure-marking を is one of the standard pattern uses of を beyond direct objects.