。
She lives in quite a fine mansion.
Literal
She [topic-は] [quite-a-ちょっとした] mansion [in-に] is-living.
ちょっとした is one of those quietly tricky adverbial-adjectival frames — literally 'a-little-did,' it functions to mean 'a decent / not insignificant / quite a / something of a' depending on context. With nouns of value (邸宅, 資産, 詩人), it elevates rather than diminishes: ちょっとした邸宅 means a substantial house, not a small one. With nouns of trouble or quantity, it can also downplay: ちょっとした問題 ('a minor issue'). Context picks the polarity. 邸宅 (teitaku) is a literary word for a substantial private residence — slightly old-fashioned, evoking grand homes more than modern apartments.