Self-mutilating/self-injurious behavior can be a symptom of a number of conditions, but suffice it to say that it is a sign of serious emotional instability. Hopefully she is receiving some mental health assistance.
The 14 year old that I described in my earlier post also cuts "Xs" into the tops of her legs and arms. Could this all be related? She states that that there was no sexual abuse but carving into skin is often associated with this type of abuse isn't it?
The technical definition of incest is not as significant as the behavior and whether it is appropriate. In a technical sense, incest is often defined as sexual intercourse between people who are closely related, or sexual behavior between people who are related closely enough that marriage is legally prohibited. So while some may not define the behavior you describe as incestuous, to some extent that is beside the point. Hopefully the parents of these two youngsters know about the relationship and can be helpful in figuring out if the relationship is sensible. Too often these days young people engage in sexual behavior much earlier than they ought, and this can lead to problems even if incest is not the issue. In general, it is fair to say that an eleven year old boy and a fourteen year old girl should not be having sexual encounters.