How does Mama respond when Linder appeals to her after Walter tells him that they have decided to move into the house? Why is it significant?

All this time, Mama has been the controller of the house. But when she didnt expect Walter to do what right for the family, she told Lidner that Walter is telling the right thing and he better get out of the house. This is the first time Mama has seen Walter do what's right not just for himself, but the whole family.