First of all, marathons take place outside of October. I assume October marathons specifically are a hot-button topic here because it conflicts with high school and college cross-country. So what? Perhaps one of the many posters who oppose teenage road racing can explain how running exclusively for your school, without doing anything outside of their sanction, 'makes a better runner.'
The young lady in question simply raced the events she was best at. (Past tense may be inappropriate since she is likely to be active going forward.) So did the list of middle distance runners you named. As other posts have pointed out, you are against teenage marathoning either because you are a school-paid coach or simply because you didn't do it yourself.
After reading varying points of view in this thread - but mostly yours, which is to say, opposed to long and non-school-sanctioned running younger than 23 - I have to say this:
Those who participate in teenage marathoning do not oppose the actions of kids who don't. I'm yet another who did. I don't remember how many posters admitted such, but it's a small minority now. I did it back when it was socially acceptable and actually considered cool. (This will be hard to believe if you're under 50.) Even with decades dimming my memory I could name several others at my school who ran one our first year there. We did nothing wrong at the time. And back then I didn't chastise anyone who didn't run any. Nor do I now. Nor, it seems, do any posters defending this young lady or pre-23 marathoning in general. We do not state that it is 'wrong' to run only 5k or 200m or whatever. Or Ryun running 1500 and mile. It's what he was best at.
The converse is not true. Those of you who did not run a marathon until well after high school or college (or still haven't) DO oppose teenage marathoning. You literally think it is 'wrong'. Just read the thread. The post I am responding to is one of dozens stating exactly that. And that's just this one thread. We do/did something (ran marathons) and have no opposition to those who act diffently. You do/did something (ran for your school cross team) and adamantly oppose other courses of action. Insecure? A thread about a great runner containing mostly criticism. I guess that's the message board......