Who is Robina from The Forgotten Daughter and what is their importance?

Robina is the slave cook at the Villa Carracinia. She makes sure Chloe and Melissa have enough to eat. She also covers for Chloe by allowing her to take her mother's Apollo statue back up to their hut. Robina has a daughter named Byrsa, whom she feeds and makes sure is healthy. Byrsa is later sold elsewhere because of her good health, and Robina is left heartbroken.