。
She's renting a room at my aunt's place.
Literal
She [topic-は] my aunt's place [at-に] is-renting-a-room.
間借り is a Sino-Japanese-style compound noun (間 'space, room' + 借り 'borrow') meaning 'renting a room' — typically renting a single room within someone else's home rather than a full apartment. This kind of arrangement (下宿 or 間借り) was once very common for students and young workers in Japan and remains a recognized arrangement. The structure ~のところに ('at someone's place') is a useful colloquial expression for someone's residence or location — slightly less formal than ~の家.