How do you deal with a person who has a persecution complex?

Everything I and my friends say to this person is taken the wrong way. I feel like we're tiptoeing round her. How do you deal with this? And if you have a persecution complex, what could I say to you that you would respond well to - to maybe stop her doing this? It's a bit of a self-fulfilling thing, she thinks everyone is against her, and everyone gets fed up of her thinking this, so eventually they *are* against her!