。
She greatly enjoys her work.
Literal
She [topic-は] work [object-を] greatly enjoys.
大いに ('greatly, very much, immensely') is a slightly literary intensifier — more elevated than すごく or とても in everyday speech, but not so formal it's out of place in conversation. Pairs naturally with verbs of enjoyment, success, or contribution: 大いに楽しむ, 大いに役立つ, 大いに貢献する. 楽しむ ('enjoy') takes the thing enjoyed with を, parallel to English 'enjoy.' Note the bare dictionary form here gives a habitual or generic reading, not a one-time act.