Wisconsin State Tenant - EX moved out but refuses to change address in drivers license

My brothers ex girlfriend had just moved out of his house a few days ago. She lives at a new address and does not have a single thing at my brother's place. He even has the keys back. They were living together for 6 years until they recently decided to separate. There is no lease or contracts of any sort. It was a spontaneous living situation type of thing. The issue is that she has his address listed on her drivers license and keeps coming back. The police say since it was a domestic situation they are bound for life? She can come and go (with police on site) whenever she wants. WHAT? What can my brother do to get her away from him and to legally stop her from stepping on his property? Eviction? Restraining order? How can he get her to stay off the property grounds? She has no bills in her name, she's not on the house title, just mail and her license. Please help. It's not a good situation and we can't seem to win again law enforcement. Thank you!