I have an 870. Well.... I have a bunch of shotguns.
The best pump gun of all time is the Winchester Model 12. But it has been out of production since 1963. It cost too must too money to produce such a fine shotgun.
Remington 1100 is nice. I like my 1100 better than Dad's Belgian Browning Auto-5. I don't know anything about Benelli or any of this new fancy stuff that is out there these days.
A gas auto will reduce recoil. Recoil pad will help also. Stock fit is real important. The guns needs to fit her.
Also gun weight will effect recoil. Bad part about that is the shooter is a woman. Lighter the gun the more it kick. Heavier the gun less it kicks. So it is a trade off between weight and recoil.
I don't buy into this business of using low base shells for self defense. OK if you are shooting quail or trap loads for shooting blue rock but it you what to stop somebody then you want to stop them.