Nico
If she needs punching, let me know. I'd be more than happy to punch her for you.
Hopefully she'll take the hint. If she doesn't, well, the police can handle it. And if the police don't do anything, also let me know. I have some methods of persuasion I can use to get her off of your case. And good idea, the professor should be aware of that.
No one needs that type of crazy in their life, so I wouldn't blame you for punching her if she goes near your sister.