。
She nodded in response to my question.
Literal
She [topic-は] my question [in-response-to-に対して] nodded.
~に対して is a compound particle meaning 'toward, in response to, with respect to' — more formal than just に and used when emphasizing the directionality or 'aimed at' relationship. Here it casts the nod as a deliberate, directed response. うなずく (or 頷く) means 'to nod' in agreement, acknowledgment, or assent — distinct from 首を振る (which can mean 'shake one's head' to refuse or simply 'wave one's neck'). Nodding is a heavily used signal in Japanese conversation, including あいづち (back-channel responses) given continuously during another person's speech to show engagement.