Who is Ulicia from Blood of the Fold and what is their importance?

Ulicia is the leader of the Sisters of the Dark, who attacked Prelate Annalina. She later becomes the false prelate that is spoken of in the prophecy given by Warren. Ulicia and the other Sisters swear a bond to Richard in order to be free of Jagang, though, they will not be forced to serve Richard or to stop serving the Keeper.