Why is my friend so stalker-ish and rude?

Hey my names April and I'm 14 yrs old. Me, my sister, my friend, and my friends sister were all SO close. But one day my so called "friend" texted me when I was at the mall with my mom saying "where are you?" and I'm like "at the mall, going to Tillys" ( it's a really popular store that all the teens go to ). She usually shops there and she says , "wow." and I'm like, " why what?" and she says "wow you don't even shop there until I did you copycat." and I said "umm.. Yeah I do.." and she says " no you don't". Like what the hell? no good friend does that to her friend. She calls me a copycat and so does her dumb sister. I mean, I never did anything to her or her sister! She's always asking me where I'm shopping at and she calls me a copycat. And one day, I added one of her friends on Facebook and she texts me saying " what the f***, ( excuse my language ) you don't even know him so why did you add him on Facebook?" and I'm like okay you know what " don't tell me who or who I can't add on Facebook okay, and does it matter who I'm friends with?" and she's like "stop adding my friends that you don't even know,copycat." I swear, I got soo pissed off. This was a text conversationg and it's funny how she can't say anything to my face. It really bothers me that her and her sister calls me a copycat. She's 14 by the way Nd goes to my hgihschool. She's a suckish friend and I don't sit on the bus with her anymore. Please tell me what you think about this whole situation and tell me if I'm doing the right thing. Thanks guys (: