From what I've read it all boils down to a situation that Ms Doherty should be more than used to by now: she hated them (the other actors) and thay hated her. Oh, and just to rub salt into the wound she retains her producer credit so she still makes more per episode than the remaining actors do. Beeatch.
I have heard that Shannon fell out with the other characters over loyalties and scripts. She wrote herself the part that killed her, but she resumes to direct Charmed and only talks to them in extreme situations. however because it is one of her ideas, she remains to keep loyalties and earns more money through this + wages for directing that she earns more money then the rest of the cast!!!