In response to hockeyfanok's comment:
I think if you check all D1 school rosters for every sport you will not find that many public school girls or boys. Pick any D1 school, go to every roster for every sport and you may find 1 out of 50 from public schools. Lets go to say BC or BU just for women sports and I think the numbers will bear that out.I do not think D1 schools really look at many public school girls, especially in hockey. Everyone lives the dream thinking their kid is the next D1 prospect. If any girl or boy can get a private school education and play a sport, good for them. The parents made the right decision for their kid
You have some good points, so I did check out a few rosters. The percentage of prep athletes vs. public school athletes varies by sport. At Brown, softball only had 3 prep athletes, and two of those were from Catholic schools. Soccer and Lacross were about 1/3 prep school athletes. Hockey was about 1/3 prep, 1/3 public, and 1/3 Canadian (often with some canadian college). What then surprised me was to look at Bowdoin, a D3 roster, and see that 13/19 were from prep schools, this may say more about who gets admitted to Bowdoin than anything else. An unscientific sampling, but I think it is neither what you assumed, that most D1 womens athletes in all sports come from prep schools, or what I assumed, that all D1 womens hockey players come from Canada or prep school.
And on the parents making the decision, sometimes that is the right decision, and the daughter's priorities line up with the parents, or, even better, the decision is driven by the athlete. Unfortunately, sometimes it can be hard on the athlete when it is the parents that think prep school is necessary, and the daughter would rather stay and play with her friends in her home town school.