I'm almost ready to put her somewhere but I just can't right now. She said her house and cell phone is bugged. When she make phone calls this man and lady are listening. They break into her house even though she has an alarm. She said they steal stuff and then when she finds it she said that they broke in and put it back. She sits and talks to Siri on her IPhone thinking that it's this man/lady that has bugged her phone. She claims that they have attached her bank by watching how she spend her money and whatever she does. I hate to talk to her because that all she talks about. She really needs help but she will not let me go to the doctor with her. She gets advertisements on her phone and she believe its the couple that's bothering her. I get so upset that I notice that I'm becoming depressed behind it. Sometimes I just leave her alone for a complete day for my sanity. Any suggestions?
You could call Adult Protective Services (APS) and ask what can be done. She may have has a psychotic break. She may have a UTI. Makes u go wonkey. Could be anything but she needs tests, labs and an eval.
https://www.wikihow.com/Baker-Act-Someone
In California it's called the LPS Act, apparently, not the Baker Act, but the process should be similar.
Why is dementia your first thought about your sister's behaviour? Have other things happened, besides this apparent paranoia, that have made you wonder? Your sister lives alone, does she?
Sorry to pepper you with questions! I hope there will be lots more helpful responses to come.