Why do you think shirley wishes to be the girl in Grandfather's story about the filial daughter and loving bride?

Well, Shirley probably wants to be the girl in Grandfather's story because she's tired of being herself and wants a taste of that filial daughter and loving bride glory. Maybe she's hoping it will bring her some good karma or get her out of doing chores for a while. Or maybe she just wants to see if she can pull off being the perfect daughter and wife for a change. Who knows, people do crazy things for attention.