I have two Remington 1100's, one is 12g, the other 20g. Very little difference in the recoil between the two guns. I think part of that reason is the 20g is a lot lighter than the 12g and does not absorb the recoil as much.
My wife has an 870 which has more recoil than the 1100. I put a good recoil pad on her gun and it made a world of difference. Best $30-some I ever spent, according to her at least.
If you get a pump 20g and do your own lighter load and a good recoil pad she may like that. Many semis won't cycle correctly with light loads, pumps won't care.
I have a VERY nice recoil setup on my O/U, but it goes for around $700 installed, more money than a lot of guns cost. I would only do this mod on a gun you plan on keeping forever.