Can I be sued for invasion of privacy by someone living in my home?

My son rents the upstairs apartment from me. He let a friend of his move in because she was homeless and needed a place to live. She caused all sorts of problems and we finally had to ask her to move out. Now she is saying that her diary was stolen and that he read it and wants to sue him over a box of magic cards, $25, and her diary. She also says that she is going to sue him for invasion of privacy. The cards, money and the diary itself is small claims court; this I know. However, I wouldn't be surprised if she didn't leave the diary out on purpose just to create drama for herself. We have had problems with her in the past as far as her making public displays of herself. She has anger issues, mental issues and is a trouble maker. She has come onto the property three times without permission and entered the apartment even though she was no longer living here. My son's other roommate let her enter once and he also let her go upstairs and ransack my son's room looking for those cards and her diary, but nothing was found. My son swears that he packed everything up that belonged to her and gave it to her. Now she is sending threatening (I call it blackmail because she is demanding the $25), and saying she will sue him for invasion of privacy, even though she committed the same thing. She has trespassed on this property when told not to. What can we do now? Does she have a case?