I wonder if daughter TOLD aunt that her parents had refused permission for this? Also, aunt is awfully close to having all sorts of permission refused to her for apparently arbitrary reasons, and has just had the freedom to do all the things she was ordered not to -- possibly wanted to share this with niece. But yeah, half-sister is still a teen with undeveloped executive function. Yeah, be angry, but be aware this is not like a 30-something doing this.