Good question, Jack-in -Box. Without any serious research (I think it does deserve some) how about there possibilities ? These are some purely logical possibilities that I can imagine, but definitely not based on any facts.
1. The girl knows, and perhaps her mother knows, but they never let it be known to the father.
2. The father knows it too, but is too ashamed to pursue the matter openly. He pretends not to know, and leads a superficially calm, composed life.
3. The father knows, and pursues the perpetrator in private, and agrees to a settlement. The monetary compensation forwarded to further his daughter's education.
4. The father knows it, but he also knows that the perpetrator can often threaten to expose the matter, thereby destroying his and his daughter's reputation. Thinking it is better to be forgotten, leaves the matter untouched.
5. The father, enraged, employs the mob for a payback Godfather style.
6. The father, unable to handle the emotional load, goes for psychological treatment, but rarely has the strength to take action, legal or other.
7. The father knows, but shrinks from pursuing it because he, too, is engaging in prostitution, so out of guilt lets the matter rest.
8. It is such an isolated incident, that few fathers know how to deal with it. They just suffer and cannot do anything.