I’m confused. How is it that the victim confessed? She’s not at fault for her abuse.
Because priests were deemed to be mandatory reporters. Teachers, police, EMS and other health professionals, etc., are all required to report instances of suspected abuse. The information received in confession from a victim would have prompted a report to initiate an investigation.
She didn't confess, strictly speaking. However in the confessional, it's not unusual for penitents to discuss with the priest their personal problems and other things that are bothering them. These days, the sacrament of Confession often takes the form of a wide-ranging chat with the priest rather than simply a sparse penitential rite where sins are recited, spiritual advice is given and absolution is granted.
This was likely one such instance of the former.
She mentioned it in confession, or she might have used the confessional as a venue to report the abuse. But anything said during a confession is under the Seal. The priest cannot reveal anything whatsoever. He cannot even confirm that he heard a particular person’s confession.