Money- perhaps Stanford doesnt offer a full scholorship and the others do. Its an expensive school.
Not money but the idea- The idea that you are one of, if not the best high school girl to come out of the us distances in a long time- and the others are given you a full ride- but Stanford isnt. To some its not a big deal , but to others it certainly is.
Her professional career- She decides to go pro.
Her future professional career- She feels a different coaching staff would be better for her to achieve her running dreams.
New coach- A new coach at Stanford- albeit one that seems very good-especially on the mens side- she may not feel comfortable with a coach in his first year at a program.
Team environment- She may be wanted to be part of a team, and perhaps feel much more comfortable with a different team(UW, ASU, Oregon) than the current team at Stanford-or feel the chances of being on a team championship are better elsewhere.
There are plenty of reasons why someone might not choose Stanford. She can go to Oregon, UW, is smart enough probably to get her degree and masters in 5 years, get into almost any medical school she wants and get a great job whereever she ends up.
Im sure the overwhelming decision maker for her and her family is where/what situation will help her running future the best- not how much better Stanford grads think their school is over anyone else.