Thanks again. There are obviously some deeper issues here, but without seeing her in-person or knowing a specific diagnosis, it's not possible to say for sure what exactly is going on. I can give you some advice as to how you might possibly address this situation, as well as some things to consider. If she has a type of PDD (pervasive developmental disorder), then her behavior is not uncommon. I can refer you to this information for ways you can possibly address her behavior:
There are some good tips that you can read about regarding children with an autism spectrum disorder who self-injure.
Another possibility is that there could be some issues of abuse or mistreatment going on at home. Often children who experience bouts of severe anger as well as self-inflicted violence and violence directed toward others are expressing their frustration and anger about their home life - so it's something to be aware of. There's more information you can refer to about self-harm in this article: http://www.kellybear.com/teacherarticles/TeacherTip44.html
Another possibility is that she is experiencing a disorder such as depression or PTSD (again, you might want to refer to this information):
Although you say it's not being seen as a mental issue, it's good to be informed about the possibilities here.
But without further evaluation, it's hard to say for sure. I would suggest that you discuss this behavior with her treatment team and/or her parents to see if there are any red flags that come up, and suggest (if your program does not currently offer this) that they bring her for further evaluation with a psychiatrist or a psychologist (if everyone is in agreement), as it's probable that she might need more intensive behavioral intervention and/or medication.
Aside from that, the way that you are currently handling the situation sounds fine, but it seems that the behavior will continue without more intense psychological intervention. Talking with her about her feelings and teaching her ways to self-soothe - such as taking a time out or using distraction through counting to ten, drawing or another creative activity- can help, but if there are more serious issues going on, then these will only be temporary fixes.
Please let me know if you have any additional questions.