Everything I have is 3rd hand information, but it sounds like Mary Cain was not a good teammate. Like it or not, high school track and field is a team sport, and the team aspect is what draws the majority of kids to it.
Imo, if you don't want to be part of a team, and won't run relays, go run for an AAU squad.
I have never had anybody who wouldn't lay it on the line for their teammates in a relay. But I've seen it with other teams. Those people aren't embraced by anybody but their parents, who are probably the ones who encourage the behavior. Thankfully I've only seen this behavior in rare cases.
of course, a coach has to be smart enough to not sabotage important invitational events for standout athletes, by having them run a 4x8 before their individual event.