She was pacing around the room. She seemed too worried to sit still.
Literal
She [topic-は] room [inside-の中を] was-walking-around. Worry [because-で] still sitting unable apparently.
A two-sentence pair. 歩き回る ('to walk around/pace') is a compound verb. 心配でじっと座っていられぬらしかった uses the classical negative ~ぬ (= ない) and the evidential ~らしい — 'it appeared she could not sit still due to worry.'