Who is Philantha Sovrit from The False Princess and what is their importance?

Philantha Sovrit is a wizard. She recognizes Sinda's power the first time they meet and immediately takes Sinda on as an apprentice. When Sinda announces she's leaving, Philantha says only that Sinda's place will be waiting upon her return. Philantha also tells Sinda that she's got more power than any wizard Philantha has ever trained, and that she will eventually master it.