Guess it all comes down to money. Unless she could get a pretty lucrative contract right out of high school it would be pretty tough to turn down a scholarship to a top ranked academic and running school.
And look at it like college coaches do. Coaches usually give scholarships based on what you are doing out of high school, don't want to count your chickens before they hatch. So although she could be the number one high school runner of all time, or even better than all the college athletes running something like 4:02 in high school. Is it really worth risking a $200,000 education if something happens and she does not ever get any better? Nike or someone could pay her a good amount out of high school and she get hurt her first year and never be able to run as a professional or as a college runner.
It is not like this is the NFL where the signing bonus alone would pay for college 10 fold.