I love Vegas, I'm very jealous of you both.
She's going to love the shops there.... (good luck)
I've seen "O" and "La Reve" and I would say that I enjoyed La Reve far more. They're both water based which is very fun. However, La Reve is in a circle, so there are no bad seats, the action is right in front of you. The show is very TALL meaning that there is stuff going on in front of you and 80 feet above you.
I would do La Reve then.
I'm not a musicals guy either but the woman and I found a great deal for a nice dinner and two tix to Phantom. I would highly recommend seeing it if it's still on. I had a blast.
Play the tables, blackjack is fun. I didn't expect us to win that much but she won 500 in one night on blackjack and it was her first time! It was a blast and she was stoked to see a good musical.
Walking around the shops is a lot of fun too, even if it's just to look. You could get some good ideas for Chrimuh.
Also, pick a night to go out for a nice dinner. I've been to several of the restaurants there and you really can't lose. I've had the best steak in my life in Vegas and some very very good seafood as well (they fly it in daily, I'd say it's as fresh as having food on the shore). There's a great place down by where you guys are staying. Lavo I think it is. I can't believe the ratings on UrbanSpoon because the food was A+ IMO.
Like I said though, you really can't lose.