^ Sounds insufferable...I wouldn't have the patience to deal with somebody like that. Kudos to you for living with her and putting up with it!
My grandpa has something to this effect but I think some of the more recent developments are a result of old age. Every night before bed and quite a few times during the day he would walk slowly around the house and look for bad guys. He would look in drawers, the refrigerator, underneath the bed, in the cupboard, under the table, the microwave...he believes there is somebody hiding somewhere who is up to no good. And if anybody asks him about it he gets incredibly mad at them.
He would also turn on the hot water every morning and night and let it run for half an hour until there's no more hot water for people to shower with. He'll stand in front of the sink and poke his hands in and out of the scalding stream of water because this "kills the germs."
When he was younger (and even now) he doesn't let my grandma leave the house or when she does, he has to be there, because he thinks that whenever she goes out she's secretly meeting up with other men. Everybody in the family knows that this is utterly ridiculous. He doesn't like her talking to people who aren't family members. He doesn't interact with people himself, either. I used to live with him when I was younger and I remember all he'd do is sit on the couch and stare at people...and whenever you stare back he'll yell at you >_<
My relatives pretty much just let him do what he likes because he's in his mid 80's already and semi-senile, but if anybody has any suggestions for what can be done it'll be appreciated as well