The girl lives in a giant house and the mother is on the top floor. Not sure if the mother ever appears as a human. I remember that a friend of hers has a party, and the chief entertainment is smashing vintage things. They travel through tubes, and never go outside. I remember she wishes she could go outside. In the end she kills or disables the house/mother and walks outside into the sunshine free.
This sounds like "Mr. Boy" by James Patrick Kelly.
The protagonist, a boy who is regularly treated to keep him at a young age, lives inside the body of his mother, which is in the shape of a 3/4 scale replica of the Statue of Liberty. He goes to a party where they bring vintage things to smash (a "smash party") and the house it's in is separated buildings connected by transparent tubes so people don't have to expose themselves to the weather. In the end, he breaks into the top floor of his house, where he's never been allowed to go before, and finds his mother. After confronting her, he leaves her to live his own life.