12 Ga over/under if you can swing the price of one. A Semi like a Beretta 391 would be another good choice. It's essentially a trade off; heavier guns recoil less, but swing like shit and take it out of their arms if carried all day. FWIW, my wife got a HK/FABARM Red Lion. It's a semi, light, and gas operated with a gas buffer to lower the recoil. I use it more than her for upland hunting. It swings like a dream, really easy on the arms, and shoots really nice patterns. Unfortunately, it only carries 3 rounds in it as the front of the tube mag is taken up by the gas buffer.

If in doubt, Rem 870 or 1187 is pretty hard to beat for the prices. If you can find an old 1100 in good shape, that's pretty good too. Can't really go wrong with anything that says Benelli on the side of it either.