I called her at six but she didn't talk to me. She might have been busy; that is why she didn't talk to me.
I called her at six but she didn't talk to me. She might be busy; that is why she didn't talk to me.
I called her at six but she didn't talk to me. I think that she was busy.
Could you please tell me differences between "Might be" and "Might have been"?