The problem is called co-rumination. It's engaged in more often by adolescent girls than adolescent boys, and far more often in adolescent girls it leads to anxiety and depression. They bond over the sharing of (and obsession with) one another's problems and often, through a mimetic process, take on one another's problems. Social media is a superhighway for this kind of communication, and exacerbates the pathological tendencies of it. Notice how the intervention of taking away the young lady's phone was a crucial first step in her recovery.