。
She served him devotedly.
Literal
She [topic-は] him [to-に] well exhausted-herself.
尽くす ('exhaust, do one's utmost, devote oneself') with に marks devoted service: ~に尽くす ('serve, devote oneself to'). Combined with よく ('well, thoroughly'), the meaning intensifies to 'served him with full devotion.' 尽くす is a culturally weighted verb — implies selfless, exhaustive effort, often associated with marital or familial loyalty (especially historically).