Several points.
1) Over 99% of global citizens are not capable of logging more than 30 miles per week without breaking down with an injury. Gals & guys who can log high mileage without injuries are not the norm.
2) Many or most female high school and college runners break down and suffer injuries past 30 miles per week.
3) Most high school and college female runners are not allowed by coaching staff to race unless said athletes return to full practice load. There are so many Park Valby-types basically kicked out of the sport because many talented female endurance athletes cannot run 5 or 6 days a week without breaking down from injuries.
4) I skimmed all five pages, no one has mentioned bone density. We don't know her bone density.
5) It has been noted on other threads that Parker Valby was a swimmer prior to 9th grade high school. Hours in the pool are like weightless hours in a non-gravity environment. A bit of chicken-egg. Are good swimmers good swimmers because they naturally have lower bone density or do many hours in the pool from age 2 to adult lower bone density?
Will 19:xx, 20:xx and 21:xx high school female 5K XC runners be allowed to train in a similar manner to Parker Valby? I hope so. Will 18:xx, 19:xx and 20:xx female college 5K XC runners be allowed to train like P Valby? I hope so. My years of observation, high school coaches have not been flexible. Did U. of Florida only make an exception for Parker Valby years ago because she was a 16:xx 5K XC runner?