Where is she?

I can't figure out where the girl went. Of all the challenges I tried to solve, this one left me hanging. Even if I did stare at her with all my concentration. I still can't get it. I think there's a clue in the sound but it's really hard to hear it right. Better to increase the volume of your speakers. Maybe you can help me with this mystery. Leave me a comment when you know the answer. Thanks.