。
She was aware of her parents' gaze.
Literal
She [topic-は] parents [possessive-の] gaze [to-に] had-noticed.
気づく (きづく, 'to notice, to become aware of') takes its object with に, not を — she noticed the gaze directed at her. The ~ていた form indicates she had already noticed and remained in that state of awareness. 視線 (しせん, 'gaze, line of sight') is a more literary word than 目 alone, suggesting a focused, deliberate look from the parents.