Who is The Sister from Welcome to the Monkey House and what is their importance?

The sister who pays special attention to Joe is kind and motherly. She walks at the end of the line during strolls and often end up talking to Joe. She seems interested in his development and wants him to grow into a sensible person. She tries to dissuade him from listening to Peter, the orphanage bully. She also tells him not to believe rumors that his father is in town. She understands that many things people say to Joe are motivated by his race.