It would be useful if you could postsome images of the mark as impressed
in the copper and silver.
Any serious s/smith will want to see samples before comissioning his
makers marks.
Also 3/16 is fine on say a bowl or larger piece of work, but on
Jewellery? no. For this , you need punches that have the design within a
1/16in sq. Can she work that small?
Most professional s/smiths have a rangeof punches to suit the work.
Also as we cant see the mark as yet, ae the punches she makes incised?
ie called skeleton? or are they in 3 D like a traditional punch?
Also before you try your punch on ferrous , have you hardened and
tempered it to a straw colour? if you havnt done either itl either break
or distort.
We await more info and images.