Daughter's mother in law is being abusive to her, what should I do?

My daughter is turning twenty four in December. Currently, she is engaged to be married to a wonderful, sensitive, and highly intelligent young man her own age. I have approved and encouraged their union from the beginning. I am happy that my child has found what seems to be true love.Unfortunately, the parents of her fiancee don't agree. For a long time, my daughter would tell me little stories about her future mother in law being "difficult". I shrugged it off as normal jealousy from an overprotective parent. However...A few days ago, my daughter arrived home from a cab ride, in tears. She ended up staying in her old room that night, telling me about the abuse her fiancee's family, particularly the matriarch, has subjected her to. Mental, emotional, and even physical abuse. What really seemed to affect her was that her fiancee's mother invited her to a quiet dinner together. Instead of going to a restaurant, she drove my daughter to a crime ridden part of the downtown area and left her there without her purse and phone. She managed to get a hold of a phone, not sure of the details, and managed to get a cab to our home.Her fiancee has been trying to call but my daughter refuses to speak to him. He told me that he is offended by what his mother did and has told her off for it. He says he chooses my daughter over her. I relayed this to her but she says she is embarrassed and angry at their family.I have no idea what to do. I don't want this woman to "win" and ruin their relationship. However, I know my daughter is an adult and needs to make her choices. I am, however, tempted to go confront her fiancee's mother. I do want to tell her off as well. Is that a good idea? What's the best choice to proceed in this situation? via /r/Parenting http://ift.tt/2dpZSFe