。
She was all alone there.
Literal
She [topic-は] there [at-に] one-person only was.
一人きり ('all alone, just by oneself') intensifies plain 一人 ('one person') with the limiter きり ('only / nothing but'). きり is the casual cousin of だけ — both mean 'only', but きり leans into emotional flavor: it often carries a tinge of isolation, finality, or restriction (二人きり 'just the two of us', これっきり 'this is the last time'). The plain copula past だった keeps the register casual.