Ok so I am all for revenge, matter of fact I am probably the queen of revenge. But why dont you try and kill her with niceness. Bring her wine, cookies, cake, flowers, what ever.....I would be do F*ing nice to her everyday that it would practically kill her. Its worth a shot. Sometimes being nice is the best revenge you can give to some one like that. Then if that doesnt work........ IDK... hire a hit man?