I have a rental property in the state of Minnesota question regarding a roommate's partner staying the night?

My roommate just got back together with his ex-girlfriend, whom I despise. She made my life a living hell when they were together in the past, and now he says that she will be here all the time. I have been looking through the Minnesota legislator trying to find a law that defines how many nights a week or a year anyone can spend at a rental property if they are not a tenant on the lease. I know that there is something out there, I just don't know what words I can use to look it up. Please help me! I am desperate and I want to find the exact law to present to my landlord so that he will back me on this. Also, is there a law about if a tenant's guest can be at a residential rental property when the tenant himself is not there? I appreciate ANY advice on what to do!!