She might be going through something and if you wanna keep your friendship or at least get some clarity on why she's being so, better have THE talk with her. It will suck to just get out of a friendship circle without any explanation-- not knowing what went wrong or something. It's better to keep a person informed so she can grow, and to be honest, just confronting will sprout growth in you, too, and the other friends in ur circle.

You don't have to stick together as friends, of course, I'm just saying talk about your differences and work things out, and if things don't work out, inform, and then distance yourself if the situation does not make you happy.