。
She's totally absorbed in her research.
Literal
She [topic-は] research [in-に] absorbed is.
夢中 literally writes out as 'inside a dream' — 夢 ('dream') + 中 ('middle, inside') — and the noun-cum-na-adjective means 'absorbed, engrossed, lost in.' The に marks the object of absorption; combined with the copula だ, it makes the structure NOUNに夢中だ, an extremely common pattern for 'crazy about X / obsessed with X.' Used for hobbies, lovers, video games, or — as here — academic work.