If you must fly into Denver and you want a real Rocky Mountain ski experience you and her are going to have to suck it up and deal with the elevation. Winterpark and Keystone are probably your better/lowest bets. Can your vouchers get you to Salt Lake City? If so, many of the resorts within an hour drive of SLC have much lower elevations.....and IMHO a better ski experience.
Traveling the States and Taking Pictures