。
She introduced me to a friend at the party.
Literal
She [topic-は] party [at-で] me [object-を] friend [to-に] introduced.
The 紹介する frame is [introducer は] [introducee を] [recipient に] 紹介する — 'X introduces Y to Z.' This is a textbook ditransitive: を for the person being introduced, に for the person they're being introduced to. The order can vary, but に + を tends to feel more natural when the recipient is shorter or topical, while を + に (as here) lets the introducee come first when their identity is the focus.