Best friend issues...?

so my best friend wont even talk to me.. and i have no idea why.. and if i talk to her about it i kknow she will get all defensive..she is being so mean to me too.. i just don't know how to tell her without her freaking out on me.. and it is so hard because alls i wants to do is talk to her.. we are varsity captains of our cheer team and it is so hard because she has been so mean to me lately.. gahh i don't knwo whast to do...