I think that's a bit obvious. She said wanna see a magic trick. Then drew her mother's faces on a bag. I don't think she has any real intentions of tracking down their mothers and killing them. I don't even think she could if she wanted to. It's like the phrase "dead to me".
Yes some kids can just be sensitive and have a small incident feel sm bigger than it is. But I don't think this is the case Fukiishi. She wasn't only abandoned but left behind with her abusive father. Abandonment is already something heartbreaking and hard to come to terms with for anyone. Let alone a six year old child, who is now left in the care of senile grandparent and an abusive alcoholic.
