Depending on weather conditions, a drive out to Snowbasin on a day with good visibility would be fun for both of you. Powder Mountain may not be worth the extra drive. PowMow is best with deep powder, but that doesn't sound like it would be that much fun for the OP's GF.
Would be good if GF were willing to take a group lesson or two. Would give the OP a little time to go explore. Both Alta and Snowbasin have very good ski schools. Midweek won't be many others in a group lesson.
I'd say Brighton would be more fun for the two of you than Solitude if you want to ski off the same lift for at least a good part of the day. The free mountain tour is worth doing since it'a all green/blue groomers, but you can learn about all the other areas and the trees talking with the host at stops.
For Alta, I suggest you park at Albion (end of canyon) on the first day. That's where the ski school is located. Start on Sunnyside to Cecret to Supreme to get GF warmed up if she isn't interested in doing a morning lesson. Note that there are blacks on Vail ridge off Sunnyside that are fun short powder shots at the right time. After doing Sugarloaf, then probably fine to check out Collins. Collins closes the latest. Note that there can be slow traffic after 4:00 on busy days (aka powder days). So either leave early or relax until after 5:30.