Title of a child's book I read years ago?

A young adult fiction about a young girl who lives in an old house with a walk in attic. In the attic there is a dollhouse which is a replica of the house she is living in. She can see into the attic of the small house where two or three past stories are acted out. One story is of two little boys who lived in the house during WWII and the second is about a little girl whose mother was kind of crazy and liked to go to high society parties. One evening the little girl's mother locks her in the attic and takes the key with her. The little girl gets cold and starts a fire to warm up but it gets a bit out of control so she hides under the attic floor boards and suffocates. The girl who is watching this is so distraught by this that she watches other parts of the house and notices that when the little girls mother left that the key fell out of her pocket in the kitchen. She goes to her kitchen and searches the cracks in the floorboards and finds the key! She brings the key up to the attic and when she sees the little girl get locked in she places the key inside the dollhouse attic. The little girl gets the key and escapes death in the attic.