I am in total agreement that Coaches need to be sensitive to body issues with female athletes. But, they are in a difficult situation. The entire point of athletic training is to change your body so it will be better in an athletic activity. So, by definition, you never have an ideal body or you wouldn't have to train.
And, while there is certainly an ideal weight for any individual runner and you can be too thin, probably at least two-thirds of college runners, male or female, would run faster if they lost 5 or 10 pounds.
I'm not saying that is healthy for already thin people, but I'd say 90% of all the PRs set by me or my serious running friends were all set when they were at their lightest weight as an adult.