。
She isn't suited for that job.
Literal
She [topic-は] that work [target-に] unsuited is.
不向き ('unsuited, unfit') is a な-adjective built from the negating prefix 不~ + 向き ('direction, suitability,' from 向く 'face toward'). The に marks the target of unsuitedness. Compare with 向いていない ('not suited for') using the verb form, or 適していない ('not appropriate for') using the kango. 不向き has a slightly judgmental tone — flagging someone as fundamentally mismatched with the work, not just temporarily unable.