Temper tantrums from an 11 year old
I recently moved in with a girlfriend of over 2 years. She has an 11 year old daughter.
When my girlfriend and I are in our bedroom (or any room) and close the door, the daughter throws a fit. I mean bad ones - slamming doors in the house, screaming through the whole house that she hates her mother, throwing things, and crying. No good reason is given for this besides - "the door was closed."
I think it's weird that the daughter never directs her anger at me too, being new to the house and all; every emotional episode seems directed at the mother. Also, when me and my girlfriend are in the room together with the door open, the kid is fine. If only one of us (doesn't matter which one) is in the bedroom with the door closed, the kid is fine.
I really, really don't understand this at all. There's nothing on the internet and no one has ever told me something like this happens. I have an undergrad degree in psychology, and still, never heard of this.
I don't get it. Is this normal?
Added info: The daughter's father is completely out of the picture. The mother's solution to the tantrums is to whoop her (which gives mixed results). I really just want to try to understand what these outbursts are all about.