Ok my friend is being really REALLY controling....help?

ok there is this girl....erm....i dont wanna say her real name....lets call her megan.Well megan is one of my best friends.Anyways we decided to do the talent show with about four other girls.Ever science we we started practicing for it she has been.....differnt. Like i had this idea we do a jonas brothers song aand dress up like the jonas brothers and she says "Wow lola,thats such a stupid idea,ur so retarded" and at first i laughed because i thought she was joking but then when i realized she waset i looked away.Also she calls herself the "leader" of the group and making decisions without concerning the whole group. What is going on with her?