I have two best friends, for this sake, we’ll call them Rose and Fern.

One day I met another girl, “Sally” and she immediately began telling everyone we were best friends, including important people who thought that Rose and Fern were my best friends. I wasn’t too bothered by this at first, until she and her father started lying.”I won first place in the Spelling Bee!”"I have this really nice video camera but we keep it in our storage unit out in New York”"Sally is the absolute best at everything” (right to my mom’s face)
etc…

We didn’t know that they were lying at first, and we invited them to go places Disneyland, Water parks, gardens, etc…and they never say thank you.
Sally once hit my mom in the face, and she didn’t say sorry.

Recently I started trying to tell Sally that she WASN’T my best friend, but she threw a fit saying things like:”Well WOMAN, I don’t care! I have a best friend and GUESS WHAT? She isn’t YOU, LOSER!!!”
and stuff like that. For this sake we’ll call Sally’s best friend Anna. I told her that Rose and Fern were my best friends, that I’ve known them since I was 2 and her for about a year, and she says.”I’ve known my best friend for three years, and she gets that I’m annoyed when other people talk about other friends!!!”

Then she left, and I was kind of sad. I called Fern, and told her about Sally, and she was quite for a while, then she said:
“I know Sally. She called me her best friend too. She still does, and won’t stop.”

I was shocked. This meant that she’s been telling three girls that they are her best friends, and her ONLY best friends, and these are only the girls I know of.

So I’m wondering, How do you get rid of a friend who can say bad things about you to the important people in your life, and basically ruin my life?