Well there’s another subtext and that is if you expect to be successful professionals in your adult life and profession you need to be on point with your message and image. People behaving like a herd of stray cats when the organization is trying to focus on achieving some PR goal makes everyone look bad.
If you don’t want to be in a sorority that’s fine but part of the package is agreeing to the group goals set by the leadership. Doing what you want and what’s most fun is not always going to align with the larger goals of the organization. If that’s not something these young women can “get” would you really want them representing your company or organization?
“No one’s the boss of me” works until you actually have a boss.
The email is over the top but the point of working cooperatively and not embarrassing the chapter with poor or self indulgent behavior is a life lesson anyone who is going to work effectively in a group has to learn.