She is, as far as the text is concerned, a wolf. Her implied race from the book is the least important thing to get right.
That said, I would shoot for a Native actress, since most of the popular theories have her as a Coyote scion.
But her
description isn't consistent with being pale-skinned, blond and blue-eyed. She was dark-skinned, had dark brown-grey hair, and--IIRC--brown eyes (actually said amber eyes that could just barely qualify as brown--i.e. wolf eyes). And when I suggested Will Smith for Harry's role, the village mob got out the torches and pitchforks--despite the fact JB himself has made the same suggestion...
But as for Coyote, while wolves and coyotes do hybridize, it's primarily due to the wholesale elimination of the former. I think there are wolf-spirit entities that would probably be closer to the role you've suggested, and they occur in Celtic as well as North American Native tradition. Since allegedly St. Patrick was the one who cursed Harley MacFinn's ancestor (and I think 'Fitz' is a Celtic word), might be worth looking into.