had questions like this before:
dragon quest swords: one hand, not the best game. look up first.
wii sports resort: more than 50% playable with one hand.
wii play: as above
wii fit and shawn white snowboarding: requires wii fit, but using legs would be nice.
vc/wiiware games: many titles do not require much hand skills, final fantasy 1 waits for commands, for example.
and i'm proud of you for having such a girlfriend, most people wouldn't see past her disability. cheers!