、。
She wished for a more relaxed life, but in those circumstances it was impossible.
Literal
[topic-は] more relaxed-した life [object-を] wished [but-が], that circumstance [in-で][topic-は] that [topic-は] impossible was.
のんびりした is the past form of のんびりする ('to relax, take it easy'), used here as a prenominal modifier — 'a relaxed-style life.' The mimetic のんびり captures a leisurely, unhurried mood; in noun-modifying position the past form is conventional even for general descriptions. であった is the formal/written past of だ — flagging this as narration or reflective prose rather than speech (the spoken equivalent would be だった). The double-は in あの状況ではそれは layers a contrastive 'in that situation, that (specifically) was impossible' — the first は contrasts the situation, the second contrasts the outcome.