I would guess, based upon the symptoms described, that the ring was not thoroughly cleaned of all firescale after manufacture. That black and green indicates oxides/sulfides of copper, the alloying ingredient of the sterling. During heating, the copper oxidizes on the surface and becomes easily dissolved in perspiration. Possibly the woman doesn't sweat as much and/or has a less acidic sweat, so she has no issues.
The solution is fairly simple, as almost no one is actually "allergic" to silver itself, though many are sensitive to copper. Simply bright dip the ring several times. Heat it to a high black heat, around 900F and quench in pickle. Do this three or four times and all the copper on the surface is dissolved in the pickle, leaving a pure silver surface. Lightly buff and you're done.
I would guess, based upon
I would guess, based upon the symptoms described, that the ring was not thoroughly cleaned of all firescale after manufacture. That black and green indicates oxides/sulfides of copper, the alloying ingredient of the sterling. During heating, the copper oxidizes on the surface and becomes easily dissolved in perspiration. Possibly the woman doesn't sweat as much and/or has a less acidic sweat, so she has no issues.
The solution is fairly simple, as almost no one is actually "allergic" to silver itself, though many are sensitive to copper. Simply bright dip the ring several times. Heat it to a high black heat, around 900F and quench in pickle. Do this three or four times and all the copper on the surface is dissolved in the pickle, leaving a pure silver surface. Lightly buff and you're done.
Hope this helps.
Rich