We already know that Naido is a disguised Diane. Perhaps American Girl is a disguised Laura Palmer too? Think about it - Laura is suddenly swept up from the Black Lodge. Where did she go? Maybe it's the Purple Room, which could be a sort of panic room of the Lodges to hide spirits. Whatever the case, there does seem to be a "extreme negative force" that she calls "my mother" trying to get in. What if she meant literally her mother? As in Sarah Palmer who seems to be inhabited by an extreme negative force? Her garmonbozia caused by grief perhaps allowed her to be vulnerable to another evil entity to enter her spirit.