Mabel did not belong to a rich family. She was one of a family of ten. They always had to be careful about their expenses, always counting the pennies. Her mother had to carry big cans the linoleum on the stairs was worn off, and there was always some minor domestic tragedy taking place.
Even when they went to seaside resorts, they stayed at lodges which never faced the sea directly, but at an odd angle, so that they had to squint to see the sea. Maybe indirectly she was still fighting with her weak economic conditions of the past, and this had made her choose the old-fashioned dress or it could have been some memories of the past that made her do it.