。
She is a very interesting person.
Literal
She [topic-は] very interest-deep person is.
興味深い stacks 興味 (interest) with the productive suffix-style 深い (deep) — 'deeply interesting,' more written and considered than 面白い. Same shape gives 感慨深い (deeply moving), 注意深い (deeply attentive). The 深い ending always implies depth or richness rather than surface-level engagement.