Should I be worried!!??

Ok well my bestfriend always goes to my house and well ,I asked her what her deepest secret was and she was like I have a crush on your brother and now when she comes over. All she wants to do is go talk to my bro go in his room and she used to act funny and stuff and now all she does is do her hair and put on makeup for him!!!!!ugh but if I even look or flirt with her brothers she gets mad should I be worried??????:(