Who is Suaro Marta from A Thread of Grace and what is their importance?

Marta is the older nun who serves at the Catholic Church under Osvaldo Tomitz. She helps the Jewish refugees in every way she can and, although gruff, is a kind and caring soul. She gets Angelo Soncini placed in a Catholic school for his protection and is a key player with Osvaldo Tomitz in helping the resistance movement, passing messages and eventually being noticed by the Gestapo for her involvement in subversive activities.