Paranoid behavior

i have a sister,age 50 who thinks people are stalking her,bugging her hot water tank and walls,every stranger that she comes into contact with,she thinks someone sent them to stalk her,she hears birds chirping when we dont,any car that is parked within 1 mile of her house,she thinks is somehow stalking her and she actually takes there license plate number down,what can be wrong with her and how do we go about helping her? thanks alot

Your sister needs to see a psychiatrist for diagnosis and treatment.