^ IMO many mothers would know. I would know if my daughter started acting different, I would see if she became withdrawn from school/social settings/friends, I would notice if she became depressed, I would notice if she acted different around her father. I would know if she was acting out because something bad was happening to her.
What I am saying is that I believe I would know if something was off. And I would find out what the fuck was going on.
The people I know that were molested/raped as children showed signs that something horrible was going on. Kids' personalities sometimes do a 180 when sexual abuse is happening.