Who is Rilla/Rachel Sherban from Shikasta: Re, Colonised Planet 5: Personal, Psychological, Historical... and what is their importance?

Rilla is Ben's companion in Zone Six. She reincarnates as Rachel Sherban, who is often jealous of her brother George, though she begrudgingly accepts the jobs that he assigns to her. When George gives her the task of raising young, orphan children with 'special' abilities, she becomes restless. Eventually, she learns of a plot on her brother's life and disguises herself as him, which leads to her apprehension by the French world police, after which, she commits suicide.