My grand daughter did exactly the same thing and my daughter was often reduced to tears, taking it very personally. Eventually, a child psychologist came to the house to observe them. (Of course, the little darling, as usually, behaved impeccably with others around!) In the end, the adviser said she was to put the child on the naughty step if, if necessary, hold her down on it, even if the child kicked and screamed. She wasn't to say anything or to look at her. This only needed to be for 1 or 2 minutes each time; children have no concept of time. It was extremely hard to do this, partly because the little darling was strong and partly because she didn't like being unkind to her! It was easier when her partner was there to help. Children hate being excluded from the attention and having her mummy turning her head away from her from that brief amount of time upset her. Sometimes, she had to return to the step almost immediately after being allowed to leave it but, with perseverance, it worked. Of course, there are now new problems; there always will be as she tests the boundaries but being calm but strong now really pays off in the end. Good luck!