The Prime is Radar's entry level boot. I am 99% sure the Rail was replaced by the Vector. The women's version (pink and white) of the Vector is called the Lyric.
For sizing reference, my daughter is a Womens 8 or 8-1/2, and is in the small Lyric...the next size up was considerably larger, and had too much slop for her. Her small did loosen up after a few uses, and goes on pretty easily when wet w/ a bit of slime.
I am a Mens 8, and have a medium Vector on a back up ski. I am at the absolute low end of the sizing range for it. Any bigger, and I couldn't and wouldn't use it. I think the medium would be too big for your wife's foot.
Hope some of this helps.