Dear Coffeegirl,
Welcome to the Bipolar Forum.

WE are happy to have you here.
i am so sorry you have had to deal with this mean, self-centered individual. the thing to write on stuff that gets delivered and you don't want it, is "refused" - the p.o. will send it back with the return-to-sender stamp added, and the "refused by recipient" ticked as well. hehe. and yes, i think you should start refusing her mail. i don't know why she tries to keep in touch with you, but it doesn't seem to have anything to do with caring or friendship, and it is only hurting you. may i also suggest you de-friend her on facebook and don't read her page.
you can't stop her from talking about people but if she writes things that are directed at you, then, you CAN nix her objective - by not reading them, or anything else. i think this is one of those cases where curiosity kills the cat.
i am sorry about your mom being unsupportive too. that is hard but we don't pick our relatives and they don't get to pick us. with your ex-friend, you have some choices.
i wish you well and i hope you will keep posting here.
~ waves ~