I am not an advocate for self harm... i probably have many regrets of my own, more than i could say. But for what its worth, it would be in everyones least intrests to get her to stop... for now. I only say this because if shes started self harming AGAIN, i asume she relapsed. And depending how long she was clean for would determine the action needed. Self harm is a way of coping, and just like people who turn to drugs or alcohol to escape, self harmers do the same, and it has the potential to become an addiction. (of course not saying self harm is the same as drugs, but it still marks and hurts the body some way).
She is not in any danger as far as i can tell, so you have a change to maybe work through your issues, and then maybe help her. I've learned that Im better helping others who are messed up when im the same, no matter if i have issues on that day. Maybe you have the strength to help her, and she might help you. It would be wise to get her to see a counciller, but unless she wants to stop self harming, its not going to be effective.