Who is Grace from Shaking the Nickel Bush and what is their importance?

Grace is Ralph's elder sister. They have always been close, and she is the one person with whom he feels he can share the truth. He turns to Grace so he can send a large amount of money home, writing her a letter that explains what he has been doing and where he has gotten his money. He then proceeds to send Grace five hundred dollars to help with the family's bills.