From the point of view of fairness, I think that special coaching is less of an issue in these cases than some other factors. For example, does the athlete have to attend classes the same number of hours as other students on her team (eg. around 7:30 AM-2:30 PM); does she practice in the same location and at the same time as her high school team (doesn't matter what she does afterward); does she compete in a reasonable number of high school meets during the season; and does she run the same or nearly the same number of times (assuming health) as the other varsity runners on her team?
What I'm starting to see happen in our state is the top runners seem to only be part of their high school team for the end-of-the-season championships meet. Sept. and Oct. they train somewhere else with a private coach; they don't run around the high school every afternoon, M-F like the rest of the kids. They suppposedly show up as much as they have to to meet the state regs, but who's gonna check if that really happens? Not only don't they race any duals or small conference meets (understandable, and I'm not saying they should), but they also don't run the big invitational meets with their hs team either. They either just train right through, or else they only run in open college meets until the state qualifiers, at which point they finally run with their high school team for the first time. Some private schools stars seem to arrange nifty special class schedules too, judging from blog and interview comments, whereby they show up to school at 10 or 11AM after an extra hour or two of sleep and a private training session. (Cory McGee used to run on the beach in the morning and then come to school later.) Meanwhile their peers had to haul their butts out of bed for the 7AM school bus and then had to sit on hard chairs for hours.
So, the regular high school star has to follow a normal high school class, practice, and meet schedule whether any of it meets their personal needs or not. They get worn out in Sept. and Oct. by racing low level meets where they're a 17:00 girl racing against 19:20 girls. Or in track, they have to run stupid 4x800 relays with teammates running 2:21, and they have to do workouts that are way too easy for them because that is what everyone else on their hs team has to do. But then at states, they run against the kid who had more time to dedicate to running, had a professional coach, who didn't have to race a bunch of stupid meets but rather could only do the ones that best suited her, etc. How is that fair?
If you want to run in the high school system, than you should train and race within that system.