。
She crouched down at the gate.
Literal
She [topic-は] gate [possessive-の] place [to-に] crouched-down.
しゃがみこんだ is a compound verb from しゃがむ ('to squat') + 込む ('to settle into'), meaning 'to crouch/squat down and stay.' The 込む suffix adds a sense of settling in or remaining.