Her ability to command respect and impose her will by pure force of personality alone in spite of being physically smaller and weaker than everyone around her was, to me, one of her defining characteristics. It was particularly important in the maturation of Nyneave.
She was small in stature, but large in power, and then lost most of her channeling ability so that the ONLY thing she had left was that aura of command. I don't think the character can be deconstructed and brought so completely down if the actress is almost six feet tall... There are lots of major roles she could fill, I just don't think they picked the right one.