My uncle's foreign bride is so mean

My uncle is a very nice and generous guy and he recently got married secretly. About a week ago, we met his foreign bride for the first time and she seemed really nice at first. But 2 days ago, I overheard her talking to my uncle and she was very mean to him. They were arguing and she said some really insulting things about our family. I want to confront my uncle and convince him that his wife is a witch. But how can I do that properly? How do I approach a middle-aged dude about his unpleasant wife?