Stacy would get the cut direct from me. I don't run anymore, but I did in high school, and many times our practice meant running in the neighborhoods near the school, or in the park. We always ran together, no one was to leave another person behind, unless it was to get help. I'm sure Coach D would have given someone like Stacy a hard time if he'd found out they'd done that to a teammate.
I wouldn't want to be around Stacy again, as after this my trust in her would be totally shot, and trust is very important to me. It's not the fact that she left, it's what she did after she left that is the most appalling.