。
I got a strong impression of her as a thoughtful girl.
Literal
She [topic-は] thoughtful girl is-である impression [object-を] strongly received.
Three things to note. 気が利く is the standard idiom for being 'thoughtful, attentive, considerate' — the ability to anticipate what someone needs and act on it without being asked. (利く here is the 'to function, to work' sense, also at work in 鼻が利く 'have a good nose' and 口がきけない 'be unable to speak' — the verb describes the working of an organ or faculty.) 印象を受ける ('to receive an impression') is the canonical collocation for getting an impression — 受ける takes abstract things one is the target of: 影響を受ける ('be influenced'), 教育を受ける ('receive education'), ショックを受ける ('be shocked'). The relative clause 気の利く女の子である modifies 印象 with である, the formal copula form, lifting the register above casual だ.