Who is Castorina from Memories of My Melancholy Whores and what is their importance?

Castorina is a madam. When the narrator was a boy about twelve years old, he wandered into her brothel, which was located near the colonial notary offices where his father once worked. One of the prostitutes grabbed him and attempted to initiate him by force into the mysteries of sex. The narrator, however, was too terrified to participate. He then became obsessed with the episode and could not forget about it, so the next day he returned to the brothel and met Castorina, who showed hin around the brothel and introduced him to the many girls who worked there.