Female appearing in G&S is a Welsh woman (6)
I believe the answer is:
gladys
'a welsh woman' is the definition.
(common Welsh name)
'female appearing in gs' is the wordplay.
'female' becomes 'lady' (lady is a kind of female).
'appearing in' means one lot of letters goes inside another.
'lady' placed inside 'gs' is 'GLADYS'.
'is' acts as a link.
(Other definitions for gladys that I've seen before include "Lady's name" , "- Knight and the Pips (Motown)" , "Girl's name" , "Female name" , "Knight maybe" .)