I have Facebook on my Xoom. Its already loaded on it. As far as Words for Friends, I don't see it in the Market and if its not showing up in the Market, that means its not available for the version of Android you are using (in this case, Honeycomb). She'll either need to contact the dev and/or wait til its updated or try to find the apk somewhere that works (not all apks that can be sideloaded onto the Xoom are functional).
BTW, we have a dedicated Xoom site. http://www.mymotorolaxoom.com