Yeah, mines a small, with a slightly longer stem. My height, oddly enough, is in my legs. But I think the small is still probably the right size for your wife.
Weird - Ash put sizes in cm, but Giant exclusively uses XXS, XS, S, M, L (for Avail).
Edit: according to Giant site, that model comes in XS, S, M, so i guess the 46.5cm is the Small