Okay, obviously it's after Christmas but in case you were still looking for suggestions, I thought I'd weigh in. I'm a "wife" who loves video games. My husband doesn't play at all. It's all me. I do have and love Call of Duty 3... Gears of War... Splinter Cell DA... and all those, but I'm thinking that shooters aren't the ones that are going to interest your wife so...
My recommendation is
Tomb Raider: Legend. I'm surprised no one else has recommended this. While I love my shooter titles, Tomb Raider is probably my favorite. I've been playing the series since the PC. I don't know if it's because I'm a girl, but the variety in it is what I love about these. There's exploring... there's puzzles... there's adventure... some shooting... just enough of everything to keep it enjoyable. And you actually get to play as a girl! As a girl gamer in a largely guy gamer world, opportunities like that are welcomed.
And for one other suggestion,
Buffy the Vampire Slayer for classic XBox (it is now compatible on the 360). What I love about this one (aside from being a Buffy fan) is the fact that you get to beat the crap out the vampires. It's amazing how much of a stress-reliever it can be to beat something up instead of just shooting all the time. This one may or may not be of interest to your wife. (oh, and do note, I'm talking about the first Buffy game, not the 2nd one "Chaos Bleeds")
And if you had a PS2 (is that okay to say here?
), I would whole-heartedly recommend Jak & Daxter: The Precursor Legacy. It's a great Mario-type title and one of my most favorite games ever.