It's a lot easier to shoot a 'too short' stock than a 'too long' one. And a lot less painful, as long as a taller person shooting a short stock remembers not to fold the shooting hand thumb around the top of the pistol grip but instead keeps it parked over on the trigger finger knuckle.
If you want a real shotgunning partner you'll arrange to make some adjustments on your wife's behalf. I see Winchester 120s/1200s marked as Sears/Ted Williams Model 200s get sold for $100 from time to time. They have wooden furniture, and usually a forearm that comes back to the front of the receiver even when the action is closed. One of those might make a good 'base gun' for a little custom fitting for your wife.
Take a look at http://www.gunbroker.com/Auction/Vie...Item=142271961
for one example. This one's priced higher than a C note but it's the same basic gun I've seen sold- and have bought myself- for that little before, and recently at that.
Getting bruised is no fun, and few people are really masochists...