She lay still with her eyes closed.

Literal

She [topic-は] eyes [object-を] closed still was-lying.

目を閉じたまま、じっと横たわっていた — まま maintains the closed-eyes state while じっと ('still, motionlessly') describes the manner. 横たわる (よこたわる, 'to lie down') is more literary than 横になる.