If Crazy “B” does not respect your instructions not to break and enter, then handling it in the family is not likely to address your issues. You could make sure the house is locked up tight when you leave. You could also go into court and ask for a restraining order to keep Crazy “B” from breaking and entering. However, there are already laws against breaking and entering. Although the police may not investigate this, I would make a complaint and ask that they speak with Crazy “B” and remind her that breaking and entering is a crime.
Mostly I would just make sure that the house is locked up and that should put an end to unauthorized “visits.”
Best of luck to you.
This response is intended to be a general statement of law, should not be relied upon as legal advice and does not create an attorney/client relationship.
You are probably best to try and handle this within the family. You may be able to sue her for trespass, but I don't hear of any actual damages. It could also be reported to the police as a break & entering, but I doubt it would be thoroughly investigated or prosecuted. If you do want to hire a lawyer on this matter, expect it to cost you more than you'll recover.
Of course this is just general information, and you can't be advised specific to your situation without knowing all the factual details. If you need legal advice, consult a lawyer in your jurisdiction.