I have a friends problem? Need help! Please!!!?

Okay, I have kind of a problem, not really that big, but whatever. Okay so I have this friend Emily and she's kind of annoying and likes to pry into other people's business. So, anyways I was on facebook and I wrote on my friend Jess's wall and said; 'me, you and Cara should have a sleepover sometime soon!!' and I guess my other friend, Emily saw it and wrote on my wall; 'hey erica, what about me for that sleepover???????' and then I went on my friend Jess's page and looked at her wall and Emily wrote 'don't forget me :)' on her wall...meaning the sleepover. It's really irritating me, because she always does stuff like that. Like, I'm going into Gr.9 next year and going to the same school as her, but not as Jess and Cara and I want to hang out with them a lot...like maybe alone once and a while. I'm not trying to be mean, I like her and we've been friends since Gr.1, but it's going too far and it's annoying me. What should I tell her?