Berthe is a little miracle, and she is Charles and Emma's daughter. Unfortunately according to everything that happened with her parents Berthe is forced into a life of poverty due to her mother's extreme debt and her both parents' untimely deaths. It seems like her parents don’t pay attention to her, and she is just a sign that yes, it is a good family they even have a child. But nothing more.
What is more, Berthe doesn’t do anything in particular, except showing the faults of her parents. She is an infant when the story begins, then she is a small child in the novel, and she simply is not old enough to act. That is why she doesn’t have many lines. However, we learn a great deal about both Charles and Emma through their interactions with her. Emma’s love/hate relationship with the little girl plays up her own insecurities and fears, while Charles’s loving neglect of Berthe at the end of the novel reveals his inability to care for himself, much less for another living being. As the novel ends, we perhaps feel the worst for poor Berthe, consigned to a life of poverty in the workhouse, who did nothing to deserve her tragic fate. And that is really sad to understand that a child will be living in complete poverty without anything and anyone behind her back.
Berthe Bovary in the Essays