This approach is doomed to failure. From the moment their daughter starts spending time with people outside her immediate family, she will start showing up in others' photos and her face will be linked to those people. Given that there's some unknown person who repeatedly shows up with certain people, the second her name leaks somewhere it will be easy to reveal her history.
Even without face recognition, disparate 'anonymous' accounts on different sites can be linked to her, as long as a few associates can be linked to real-world people [1].
Even without face recognition, disparate 'anonymous' accounts on different sites can be linked to her, as long as a few associates can be linked to real-world people [1].
[1] http://www.academia.edu/1518346/Link_Prediction_in_Highly_Fr...