Why is my friend acting weird.?

okay me and her are the best of friends. but for the past two days she has been acting really weird. like she wouldn't talk to me [just ignore me] she doesn't hang with me at recess or anything like that, but she always hanging with this other girl [we r both kool w. her] but when they're together she just ignores me and give all her attention to her..... So why do yu think she is mad or whatever?