。
She asked me who arrived first.
Literal
She [topic-は] me [to-に] who [subject-が] first arrived [question-の] [quotative-と] asked.
An indirect question with an interesting twist: the embedded question 誰が最初に着いたの ends in the casual question particle の rather than the more standard か. The の ending gives a softer, more conversational feel — common in casual speech and traditionally associated with women's speech, though increasingly gender-neutral. The と is the quotative particle linking the embedded question to the verb of asking. Note that subject-marking が (not は) is required inside an embedded wh-question — it picks out 'who specifically' rather than introducing 'who' as a topic.