Who is Drina from Plain Kate and what is their importance?

Drina is Linay's niece, and a member of the Roamers' clan. Drina and Plain Kate become quick friends, and when Plain Kate tells Drina about the loss of her shadow, Drina offers to help her. Helping Plain Kate, however, causes Drina to be attacked. Drina bares no ill-will, however, and later helps Plain Kate stop Linay.