Tina and Christie are both nicknames for Christina. The doll and the child share a name, so among many other interpretations it could be argued that the doll is a proxy through which Christie expresses hostility toward her stepfather and protects her shy, frightened mother. See more
Of course, we all know dolls can't really talk, and they certainly can't commit murder. But to a child caught in the middle of turmoil and conflict, a doll can become many things: friend, defender, guardian. Especially a doll like Talky Tina, who did talk and did commit murder - in the misty region of the Twilight Zone.