Madame Gu had thought that what Gu Chaoyan was going to ask for was her own defence, so she could have an easier time in the Gu Mansion. She had not expected that she was demanding to get the dowry her birth mother had left her.
According to the land's law, the girl's dowry when getting married belonged to her only, and it was something to be dealt with by the girl's children. Ms. Lin died at a young age, so the Gu Mansion had been taking care of the dowry. According to the laws, the dowry should be her own daughter's, namely Gu Chaoyan's despite her early death.
However, Ms. Lin's dowery was quite exceptional.
The Lin Family was in the medicine business and had relations with the imperial court. So the dowries were quite abundant. The Gu Mansion could be so wealthy right now mostly because of the dowry from the woman.