。
She just laughed it off.
Literal
She [topic-は] [just-ただ] [laughed-off-一笑に付した].
一笑に付す (issho ni fusu) is a lovely Sino-Japanese set phrase, literally 'to assign / consign to a single laugh' — meaning 'to laugh off, to dismiss as not worth taking seriously.' The verb 付す (to attach, assign, submit) is rare in casual modern Japanese but survives in fixed expressions like this and 注に付す ('to relegate to a footnote'). The 一笑 ('one laugh') compresses the gesture: it took only one short laugh to write the matter off. ただ here is the adverb 'merely, just,' framing the dismissal as the entirety of her response. Slightly literary register.