。
She did nothing but stare at me for a while.
Literal
She [topic-は] for-a-while me [object-を] gazing [nothing-but-てばかり] was.
見つめる ('stare, gaze, fix one's eyes on') is a more weighted verb than just 見る ('see, look') — it implies sustained, deliberate focus, often with emotional weight: a gaze of love, longing, anger, or scrutiny. ~てばかりいる ('does nothing but') frames the staring as exclusive — there was nothing else happening. The combination of しばらく ('for a while'), ばかり, and the past continuous いた makes the staring feel uncomfortably prolonged, the kind of gaze you remember as charged or unsettling.