。
She's absorbed in her studies.
Literal
She [topic-は] studies [in-に] absorbed is.
勉学 is a more literary/formal synonym of 勉強, emphasizing scholarly pursuit. 熱中する is 'to be absorbed in' — a near-synonym of 夢中になる, but 熱中 emphasizes heated enthusiasm whereas 夢中 emphasizes losing awareness. The ~ている marks the ongoing state of absorption.