。
She lost her new watch.
Literal
She [topic-は] new watch [object-を] lost.
なくす means 'to lose (an object)' — not to be confused with 亡くす (also なくす, 'to lose someone through death'). In writing, the object-loss sense is often written in kana (なくす) while the bereavement sense uses kanji (亡くす). This is a simple, direct statement of a mishap.