。
She served him.
Literal
She [topic-は] him [to-に] served.
仕える ('to serve, be in service to') is a verb specifically for the deferent service of a master or higher-ranked person — historically applied to lords (主人に仕える), priests serving deities (神に仕える), or modern figures of authority. Compare with サービスする (loanword, generic 'serve, provide service') and 給仕する (table service). The に here marks the served party.