'Fraid I have to agree that yes, she was. The poor employee couldn't do anything -- couldn't even walk away -- so she was deliberately targeting somebody who couldn't fight back. And that's not even remotely fair.
As for the carding, as others have said, what's the store's policy? If they have to card everybody, then that means your mom too. Mine, who is now 78, was asked 5 or 6 years ago for ID when she was buying cigarettes at a large supermarket that has (understandably) flung up its corporate hands and said, "Screw it, we're checking everybody from now on." She was dumbfounded but pulled out her ID and got her smokes.
These days, anybody who doesn't carry some form of acceptable ID on them has only themselves to blame when they want to buy something that's age-restricted and can't get it.