Multiple Personalities Support Group
Dissociative identity disorder is a diagnosis described as the existence in an individual of two or more distinct identities or personalities, each with its own pattern of perceiving and interacting with the environment. At least two of these personalities are considered to routinely take control of the individual's behavior, and there is also some associated memory loss,...
Based on my experience, I'd try telling her that you love her, but are going to put limits on her behavior, that she isn't allowed to kill anyone.
Reply to what she says in statements that are opposite positive statements.
In my case this caused my introject to sort of start repeating herself...then shut up in confusion.
...Mine has had a temper tantrum where she stomped off in my head, shouted "I HATE YOU!" and slammed a door in there
o.O