。
She decided to quit her job.
Literal
She [topic-は] job [object-を] quit [decide to-ことにした].
~ことにする ('decide to do X') is the standard frame for personal decisions. The こと nominalizes the verb phrase; に marks it as the target of する. Distinct from ~ことになる ('it turns out that, becomes the case that'), which describes a result or outcome that arises without the speaker's direct decision — a useful contrast for separating personal choice from external circumstance. 辞める is the standard verb for leaving a job, distinct from 休む (to take time off) or 退職する (the more formal/Sino-Japanese 'retire/resign').