Lots of good points above. I have a Beretta Ultralight 686 12 gauge that tips the scale at only 5 lbs 11 oz, and it kicks like a MULE. Unlike your wife (thankfully for you! lol!), I am 210 lbs and I STILL don't like shooting clays with it. The difference with my regular weight beretta 687 OU (just shy of 7 lbs) is very noticable - much nicer to shoot. The difference with my Xtrema semi is even MORE noticable. My buddy has a Citori that weights a million pounds, and the recoil on that pig is almost negligible. So, I think the best way to balance weight and recoil is to get her a semi. If not, I would shoot for something in the 7 lb range. Sure, it's a bit heavy for such a small person to tote around, but it won't knock her around so much either. If you go with a semi you might also be able to get her some additional recoil-reduction features, like Kick-off or whatever. Either way, obviously a good recoil pad will be key, but I would be careful what you get installed. When I bought the ultralight (here on the EE) it had a very "squishy" recoil pad installed. That was good for recoil, but it was also very "grabby", always catchign on my clothing etc... I had to switch it up for one of the pachmayr ones with the no-snag heel on it (more recoil, but no annoying snagging). I also picked up a vest with a leather shoulder and a sleeve for a gel pad inside. Makes a difference as well, even as "well padded" as I am already. Hope this helps - good luck.
Dave