Maybe you can hint to your sister to be more involved in her daughter's life. Try directing her into the direction of finding out. Your not telling her, but your also helping her see what's going on.

As for why your niece cuts herself; I find no other reason to do it other than to relieve stress. When I'm stressed out from all the drama in my life(oh god I hate drama) I cut myself, I do it because it calms me and it makes me feel like I dont need to care and all the emotional pain goes away. Even though the next day I go to school, I go feeling monotone and just with out care and things just tend to go my way:S.. THat may not always happen but it does for me but Ima make sure I dont abuse this miracle thing.. but that could be why she's doing it too! Im just trying to relate>.<

Coming from someone that used to cut, where she cuts and how deeply says a lot about why she cuts. If she merely cuts the back of her arms or her legs, keep an eye on her but don't go raising red flags. Many people around her age cut because they're overwhelmed and wish to feel some sense of control over their lives. If she cuts the insides of her arms or her wrists, it could be a sign that she's suicidal. Regardless of what you do, be gentle with her. If you're concerned about her trusting you, offer to be someone she can talk to. If you serve as someone that's there for her but doesn't tell unless she's absolutely in danger of losing her life, she's likely to tell you more about what has brought her to cutting.

Become more involved in her life! Get to know her better. Though it's common for girls her age to cut, she probably is doing it because she's lonely or overwhelmed. Take her out, spend some time with her, and just generally be her friend. Even if she doesn't tell you about why she cuts, you might help to lessen the load on her shoulders.

if I were you I would tell that to her mother. But, everytime I tell something to another person, he/she gets very VERY upset. But, anyway I tell them. The problem is how she'll react. But, if you tell your sister that her daugther is cutting, it's for her best...I suppouse you know better her than me. Can you rely on your niece?..Do you know she's really saying the truth?. I would wait some days, if she continues cutting, I would tell her mother...sorry, I can't give you much help...I can only tell you what would I do...

I think you should just hint to her mother because her mother needs to find out on her own. I cut, and the reason i do is because of family stress. my mom puts a lot of stress on me and so does school, maybe you should ask her about why she cuts, to try and understand more, and then decide if you should start the hints.

she is in pain and cant feel outside her heart she cuts to feel that pain and not her internal pain its hard to decide to tell and she may hate you for a while but u telling is the only way to make her better. try to get her to tell first and no matter how much she hates you dont leave her. she will push everyone away and she will fight to keep u all out but what she needs the most is to be around people who are suffering the same as her. u will never understand her pain like she needs but u can lead her to the place where she can see shes not the only one and that is the most important thing u can do for her. love her no matter how hard it is and be the bad guy because that is what family is supposed to do. if u dont get her the help she needs now she will never learn that there are ways to feel better without hating yourself. i used to be a cutter and its hard to let go of the mentality that u have to hurt to feel better. shes just searching for a way to let go and be free. if you love her help her now befor its too late.