。
She's completely satisfied with her new job.
Literal
She [topic-は] new job [with-に] completely is-satisfied.
すっかり is an adverb meaning 'completely, entirely, thoroughly.' It emphasizes the totality of her satisfaction — not a partial or reluctant contentment but a wholehearted one. Unlike まったく or 完全に, すっかり has a warm, colloquial feel that suits personal emotions well.