Originally Posted by
The Fantastical
I agree.
It's better to be hated by your cousin in the short term and for her to get over this than to be trusted by her and watch her get worse.
Tell her that you have to tell someone though, explain to her this isn't a secret you can keep.
I think she needs help now, when she is twelve. If a problem is tackled sooner, the behaviour will not get as ingrained - be easier to change.
While you do make good points, my fear would be that she wouldn't talk to anyone at all after her parents are told. She seems to trust the OP a lot to tell them something like this, if she feels betrayed by her then how can she be expected to trust anyone?
Not to mention we don't know how her parents will react, a negative reaction could be very harmful-- Especially since the OP promised not to, I think that they need to either get their cousin to tell, or get their cousin's permission to tell her parents. Breaking someones trust in you can be very bad when they're already having emotional problems.
She definitely needs to tell someone, but doing it behind her back
could do more harm than good.