Mother of Groom Refuses to Listen to Bride and Groom's Opinion of mog Dress

My future mother in law (mother of the groom or MOG) refuses to listen to the MOG attire guidelines and is instead purposly trying to get a rise out of myself and my fiancé. The first dress she chose was a cream color even though she knows your not supposed to wear white to someone else's wedding. Her second dress she picked was a peacock dress incorporating every single one of our wedding colors (blue, purple, and green - picture included in post). Finally her last dress pick was a dress she lent to my fiancé's most recent ex of 4 years to wear to there 8th grade dance (the MOG still has a whole album on FB of my fiancé's ex in the dress with him labeled ".... and his love"). She refuses to buy a new dress and said her money could go towards something better. Mind you she's not paying a single penny towards any of the wedding including the reception. I've even sent her other dress options and have had my mom intervene, but nothing seems to get through to her. Does anyone have any advice on how to get her to wear something else?