Ring little Katharine who is satisfactory (4)
I believe the answer is:
okay
'is satisfactory' is the definition.
('okay' can be similar in meaning to 'satisfactory')
'ring little katharine' is the wordplay.
'ring' becomes 'o'.
'little katharine' becomes 'kay' (I've seen this in other clues).
'o'+'kay'='OKAY'
'who' acts as a link.
(Other definitions for okay that I've seen before include "Passable" , "Yes; satisfactory" , "Agree" , "Give approval to" , "All right; sanction" .)