In the story "The Doll's House," why is Isabel allowed to be the one to break the news of the doll's house to the other children at school?

Isabel is allowed to tell the other girls about the doll's house first because she is the eldest. She says that her sisters can join in after but that she is to tell the news first. Isabel is a bossy girl and she thinks that she is always right. She also says that her mother allowed her to choose who is going to see the house first. The younger sisters, Lottie and Kezia, know the power of being the eldest daughter so they do not complain.