Gun ownership questions..

I doubt they'll even be at the store to begin with.

They were sold with the store and all of its contents - not her issue any longer

What store is it? I'll go with you when you ask! I think you're SOL.

How would she be responsible?

There's no "registration" of guns. So if she gave or "abandoned" them to the new store owners, they're not hers anymore.

If she's worried that someone would hold her liable if they were ever used to hurt someone, stop worrying. That's preposterous.

Aaron

Those guns are long, long, long gone.

There is no registration, and unless she knowingly sold/traded/gave away the shotguns to a felon, then she's got absolutely zero to worry about.

I think that you are out of luck. Imagine that you are the current owner and some guy comes in claiming to be the son of the guy that owned the store years ago and wanted some property that was left behind. As the store has changed hands a couple of times this request is even more unlikely to work.
Just let it go. The shotguns are gone.

Having sold two businesses I can assure you they're history. Generally a sale will involve a building and contents, and that includes everything. I even had one buyer come over with a video camera in advance of closing the sale so he could video everything in the building. Each desk drawer was opened and filmed, all the inventory, all tooling, all of everything. Of course it all depends on the terms of sale.

Then you said there were several owners after the original sale. Realistically, one of the intervening owners took the guns home or sold them. Fuggitaboutit.

Those guns are gone..

Too late! You won't be getting two more shotguns for your collection.

We sold a house many years ago and I inadvertantly left a duffle bag in the attic containing my old Army dress uniform and some other surplus gear. A few years later when I realized that I'd forgotten the bag I contacted the buyer who told me it wasn't there. That's exactly what I'd expect the new store owners to say. Close the book and don't worry about it.