I think my mother has paranoia, how do I help her?

I think my mother has paranoia because she thinks that everyone is working against her. When she loses something, she thinks that someone deliberately stole it from her. Some of the things that she believes are quite frankly ridiculous and yet she seems to be convinced that it's true.
When I try to tell her that she has a problem or say things as it is, she gets very defensive and she will say that I'm not her daughter because I'm not taking her side of things. I'm just trying to be sensible!

I want to help her, she is a good mother, but she clearly has problems and I don't know what to do...any ideas are appreciated.

Can you get your mother to visit her doctor, or you could talk to her doctor if she is unaware and paint him a picture of how things are.