。
She borrowed his idea.
Literal
She [topic-は] his [genitive-の] idea [object-を] borrowed.
借りる ('borrow') applied to ideas — extending the literal sense (借りる money, books, tools) to abstract things. The metaphor works in both Japanese and English. Note that アイディア (loanword from English) is the standard Japanese word for an idea/concept; less formal alternatives include 考え or 思いつき, more formal ones 概念 or 観念.