。
She settled into the easy chair.
Literal
She [topic-は] easy-chair [in/on-に] hips lowered.
安楽いす ('easy chair, armchair') is a half-Sino, half-native compound — 安楽 ('ease') + the native いす ('chair'). 腰を下ろす ('lower one's hips, sit down') is a fixed idiom — literally 'lower the hips,' a more deliberate and almost ceremonial way to describe sitting compared to plain 座る. The pairing of an easy chair with this composed motion paints a quiet, settled scene.