。
She stayed at her aunt's place yesterday.
Literal
She [topic-は] yesterday aunt-honored [genitive-の] house [at-に] stayed-overnight.
泊まる ('to stay overnight, lodge') is distinct from 滞在する ('to stay, sojourn' — longer, more general) and 残る ('to remain'). 叔母さん carries two layers: 叔母 ('mother's younger sister' — Japanese kinship terminology distinguishes elder vs. younger siblings of one's parents through 伯/叔, though casually the distinction is often blurred), and the honorific さん softening the address. 叔母 is technically aunt-by-younger-sibling-of-parent, while 伯母 is the aunt-by-elder-sibling — a distinction that survives in formal writing even where speech tends to merge them.