Maid of honor bringing a date noone knows.... where does he sit, whats his involvement?

My maid of honor should go down in history for causing the bride the most stress. She hasn't planned nor helped plan 1 thing but is constantly asking me questions she should either know the answer to or that are so medial I want to scream. Last night she told me this guy, whom she isn't dating,has never even gone out with,is who she is bringing to my wedding. For starters I said she could bring a date but assumed she was bringing someone I at least know. My fiance dispises her because she constantly makes jabs at him, he is in the Navy and is a damn good guy. She constantly makes comments on how "he doesn't understand bc he didn't go to college"