How do I get rid of this girl?

I'm a girl. This girl used to be my brother's girlfriend, and during the 2 short months that she was with him, she managed to convince herself that I was her best friend in the entire world and confided everything about their relationship to me. I didn't really want to know what was wrong with my brother, and sometimes defended him. After the break-up, I didn't offer any consoling to her (i.e. "Oh, he doesn't deserve you, he's a monster, he shouldn't have broken up with you, he didn't know what he had.") because it wasn't true. They just didn't fit together. However, she proceeded to go through my friends list on Facebook and friend all the friends I normally talk to or hang out with. Though she barely knew my best friend, she somehow squeezed sympathy from her and got her phone number and called her and told her a lot of lies about my brother (which my best friend knew to be false since she actually knows my brother) and "married" my best friend on Facebook. She comments on all my photos, posts, wall posts to others, and it's really getting annoying. I don't want to un-friend her, because then she'll constantly text me asking why I'm not her friend, and if I don't answer her texts, she'll text/call my best friend and blow the whole situation out of proportion and possibly turn my own best friend against me. My parents don't know what to tell me, my brother told me to ignore her and sh'ell go away, but she hasn't, and I've talked to my best friend and she says she's a bit scared by how over dramatic and manipulating this girl is and wishes she hadn't ever talked to her in the first place. I really need help here, and please don't swear in your answers. Thank you!