Mom Dislikes Fiance and Family

Hi Brides! I got engaged in July, but my mom really dislikes my fiance. Everytime I try to mention anything to her about planning, she comes up with ridiculous things from years ago (like saying some mean messages she sent from her phone was really my fiance hacking into her phone and sending them). I really can't stand her constant negativity toward my fiance and his family and I want to be able to actually plan my wedding. Has anyone been here before? I would appreciate any advice!