。
She's fed up with the job.
Literal
She [topic-は] that work [target-に] fed-up doing.
うんざり (or うんざりする) is a 擬態語 (state mimetic) for being thoroughly tired of, fed up with, or sick of something. ~にうんざりする takes に to mark what one is fed up with. The progressive ている describes the ongoing state — she's currently in the fed-up condition, not just briefly annoyed. The word captures a heavier kind of fatigue than just 疲れる: not physical exhaustion but emotional saturation.