Who is Katrina in Gathering Blue by Lois Lowry?

We first meet Katrina at the start of the novel when Kira is watching for her spirit to depart at the Field of Leaving. Katrina worked as a seamstress, caring for the robes of the Singer. It was Katrina's diligence and protection that allowed for Kira to live when she was born with a deformed leg. Her mother raised her alone.