Cousin thinks family is part of internet conspiracy

Members of my family, including myself, have been receiving accusatory texts from a cousin saying we are part of a bizarre internet conspiracy against her. She claims we all know the person who has orchestrated the consiparacy and that we are in on it with him. None of us know the person she is talking about and each denial of knowing this individual is taken by her as an admission of guilt. She claims the local police department is in on it and even disappeared for ten days last year so that she could attempt to get the conspiracy under control. She is highly intelligent (MENSA) and often talks down to all of us. I received text messages from her yesterday that went like this:
"Hi, thanks for the card! You are always do such nice things! Say hi to Bert for me! Talk to you on the net!"
Me: "Glad you got it! I don't know anyone named Bert. Hope you're well! Love you!"
"Oh, I thought you knew him. He said he knows you, but people can say anything on the net. I think he's someone you and I could have an honest conversation about."
Me: "Name, I don't know anyone named Bert and never have. Is this in relation to your internet issues?"
"How did you know I have internet issues?!?!? You probably don't know Bert, or you wouldn't buy into his bizarre plan. At least about me, anyway! I could show you all of the stuff I have saved, including IP addresses and cell numbers."
Me: "You have been talking about your internet issues for the past two years. Those issues are part of the reason you left town last year."
"Anyway, I love you. And I forgive you."
Me: "Hope it all works out! I haven't done anything that needs forgiveness. Take care! Love you!"
"You are doing something that needs forgiving right now!"

??????????? I haven't talked with her since, but I am a bit concerned. This conspiracy theory has been going on for a couple of years now and I'm a little afraid of what she may do to someone if she thinks they are part of this plan. I don't think this Bert person really even exists and it's a really strange feeling to have no idea what someone is talking about when they are accusing you in a roundabout way of being involved in some farfetched scheme. She thinks the people involved want her to be their sex toy and says they want to "ravage her body".

How do my family members and I deal with this? BTW, there is a lot of mental illness in the family...

For our family member, we were told by the experts not to engage in talking about the delusional thoughts. When the accusations were angry and causing us emotional turmoil, we were advised to tell her we won't talk about it, and like speaking to a child, tell her we won't visit or have her in our home if she continues. Since then, I've also read that stating "I don't allow unsafe behavior here" might help to quell fears, in addition to curtailing the talking about the delusion, and keeping to more pleasant and encouraging topics.

But hearing about the suspicions from the delusional person also helps to monitor the thinking. As a family member, I need to know if I need to phone the crisis line, or the physician, or the police again, to ensure the safety of everyone.

It is hard, because unfortunately, talking about the person's recent statements sometimes dominates conversations we have with other family members because we are all concerned and we all need to communicate about the person's state of mind, to watch for anything dangerous.

Hopefully someone in your family will volunteer to be a coordinating person, gathering dates and statements and or actions of the delusional person. That information could be helpful if the need arises to inform a doctor or court. A coordinating person might also be the one to phone a crisis line or police if the behavior becomes dangerous to the person herself or others.

From what I read, the intensity and frequency and agitation of the thoughts might go up and down, even after treatment, though it seems most don't realize the thoughts aren't real. My family member is still angry that the rest of us don't 'believe' but has calmed a lot and only infrequently mentions the fears and suspicions.

Good luck.