Who is Drousula from Corelli's Mandolin and what is their importance?

Drousula is Mandras' mother. Over the course of the novel, she and Pelagia become close friends, and when the doctor is taken away and Pelagia is left alone, Drousula moves in with her. She later opens a successful restaurant. Drousula disowns her son when he assault Pelagia, and she helps Pelagia raise the young Antonia.