I tell all my tenants that failure to follow the lease to the letter will result in immediate eviction; I make NO EXCEPTIONS and neither should you. The ex-husband, girlfriend, and kids should never be allowed to spend the night. Do you have insurance on that building? Just know if any of them get seriously injured or even die, you don't want that to come back on you. Tell your tenant (if you can pull her aside long enough to have a conversation with her) that these extra people have to go or she goes!