These situations are probably more complicated for a team to handle than we think. To avoid lawsuits and privacy violations, university staff probably can't single out a particular athlete for medical testing/nutritional or psychological counseling just because they think she looks dangerously thin. They probably have to make all the girls get their heart, BMI, bone density, etc. tested in order to check on the one they're actually worried about, unless the girl collapses or something.
Secondly, it's complicated for concerned teammates to say anything. It's not their business, they may not be good friends with the person, and they assume the coaching and medical staff are or should be on top of it. Also, any comments can be viewed as stemming from jealousy. On a friend's team, this freshman girl showed up as an xc walk-on and beat many of the recruited girls. But she looked unhealthily thin. The girls were really unhappy about her representing the team looking like that, but were afraid of it seeming like sour grapes if they talked to the coaches. In fact, the jealousy accusation got thrown around when one girl did make a comment. Meanwhile, the coaches had little incentive to stop her from running when she was doing well. Within 2 months she was in the hospital for a dangerously low heart rate due to anorexia. But they only made her take a few weeks off to recover and she was back for spring season. Wow.
Lastly, more than 50% of college girls have eating disorders, and among runners the percentages are higher. So if a coach were to make all his girls with active eating disorders or managed disorders stop running, he wouldn't have team. Meanwhile, normally slender girls who get their periods but don't look like skeletons, can have a really tough time competing because they are carrying around more weight. To them, eating disorders seem like a form of cheating. Like doping or cheating in school, ED's usually comes back to bite the person in the form of stress fractures or heart problems or mono, but in the mean time they often have terrific success.
And heck,