riding ice is more about keeping your edges tuned, and having proper form more than about anything else. A stiffer board can be nice for higher speeds due to the stability of a stiffer deck. The Never Summer might fit your needs but it was made for our CO slopes as well. You might want to check out one of the board manufactures that do the Magnatraction if you are worried about holding an edge.
Size wise anything from a 151- 156 would do for your wife.