The AA low recoil/low noise loads I refer to are 26 gram at 980 fps and shoot very soft, if you/she goes for a 12 gauge then I'd highly recommend these. If you hand load then there are lots of published low recoil loads to chose from.
As Rob mentioned above, 12 gauge 1 oz loads at 1200 fps stll produce as much recoil as 1 1/8 oz loads at a slightly slower velocity so don't get fooled by the payload, you have to look at the speed too. The Winchester Super Target 1 oz 1145 fps loads are some of the softest target loads available too.
You will have to show your wife a bunch of different guns and have her try them out and it's important that you let her decide which gun to go with. An o/u or a 12 guage may be too heavy but maybe not, let her decide that.
My wife is 5' 5" and weights 130 lbs and she handles a 12 gauge Beretta 682 o/u very well and has done for years. She shoots regular target loads without any complaints but these guns mitigate recoil quite well. I've seen lots of other smaller women handling o/u guns very well too so again... let her decide.
I started out my daughters on a Remington 1100 20 guage LW and that was a good choice. These guns are fairly heavy and the gas systems mitigate recoil well. Now that my grandkids are just about big enough to shoot I wish that I hadn't gotten rid of that gun.