Scolding another person's child

My niece came over to play last night. She is a few months younger than H but they would be in the same class if they were to enroll in school together. She is a tad smaller in size than H yet her personality and stubbornness matches that of a 50 year old woman going through menopause. One inexcusable behavior she exercises is grabbing a toy, marker, paper, what have you, from other children. These past few weeks, H & T have been the target of her snatchings. They are not used to the unsolicited aggressive behavior. H has cried many tears over a snatched Play Doh cutter, glitter pen, toy dogs, etc. The one good thing is that when her mother, my SIL, is around, she gets reprimanded and scolded for such acts. She has been quick to condemn, judge and punish so that I would not have to intervene.

Last night, however, I picked her up from grandma's house and brought her over after the 2 girls had finished their baths. So no mom, my SIL. Mike was home as well. He witnessed her snatchings and instrusive mean-spirited behaviors with much disdain but refrained from saying anything to her. When she asked him to put in the Cinderella DVD, he agreed hoping she would sit quietly and watch the movie. She proceeded to move around the room touching everything H had her hands on. She even went as far as stepping on the ukelele which was lying around on the floor. That made Mike tell her to go home. She burst into tears at which point I whisked her up and tried to packed her in the car. Even in her crying stupor, she asked to be put down so she can climb in on her own and buckle her seat belts without assistance.

My SIL called me last night to profess the hurt she felt that her daughter was scolded by Mike. I told her it was inexcusable but this is the way Mike parents children, especially our own. That he didn't do anything out of the ordinary. He would have told H or T to go upstairs instead of home. He has no tolerance for rude behavior especially one that seems so purposeful and premeditated. I think my niece has had too many people scolding her this trip. I have withheld my own tendency to scold, chastise, etc. because I felt she needed more reasonable boundaries through non-judgmental words. She usually doesn't listen to that either but I have faith that one day, something would click. Mike doesn't operate that way. One, two three strikes with zero tolerance makes it difficult to live up to for 3 and 4 year olds. But this is my household right now and daddy has to have his rules too. I had little to say in terms of comforting my SIL's anguish.