She left the room with her eyes cast downward.

Literal

She [topic-は] downcast-eyes [manner-がちに] room [from-から] went-out.

伏し目がちに ('with downcast eyes') — the suffix ~がち means 'tending to, prone to.' 伏し目 ('downcast eyes') + がち + に creates an adverb describing her manner of leaving.