What would you do if your daughter is jealous of the attention her baby sister is getting?

my friend, opal, had been a single mother for a long time. penny was her only daughter and she meant the world to her. then she married a man named barry. then they moved to a new neighbourhood. it was far away from the place they used to live. penny wasn`t very happy about that, despite the fact that she finally had a father. her biological father had ped away before she was born. she and barry are still getting used to eachother. opal is now pregnant, which is worrying penny even more. getting used to a new dad is difficult enough. she is also scared that her new baby sister, whom they have planned to call sophie, will be smarter and better than her, and then her parents will not love her anymore. penny doesn`t like the changes and wish things were like they were before her mother remarried. i am sorry to have to say this, but she is a selfish child with a jealousy nature. she isn`t getting the same amount of attention she used to receive, and that is very hard on her. she doesn`t want to share her mother with anyone. she wants to have her all to herself.