I have had poor luck shopping online for my wife's boots... get to a Cabela's, Scheels, Bass Pro, or something similar and let her try them on and pick them. You may have luck there in Cheyenne at Sierra Trading Post?
The big issue I have had is I always seem to select traditional styles in boots and she always ends up going for a hiking style, lower top boot. With gaters these actually do a nice job even in deep snow if you pick the right boot. Spare no expense on her boots imo... a wife with cold feet isn't a fun hunting partner.