This girl only contacts me to complain?

one of the girls i know used to be my bff in elementary til she ditched me for mona and lily. we now go to seperate schools, but she only emails me to complain about these girls and what they did to her. ex: hacking her fb, spreading rumors about her, and other crap. and she still chooses to hang out with them, and they continue to do mean things to her, and she complains to me. and i do not want to yell at her, and i tell her not to hang out with them. but she chooses to anyway. and i am not her venting box, and i do NOT want to listen to her moan. how do i tell her that i really dont care?