For her the cockney had jellied eel (5)
I believe the answer is:
adele
'for her' is the definition.
'cockney had jellied eel' is the wordplay.
'cockney had' becomes ''ad' ('had' said with the 'H' dropped - a cockney accent.).
'jellied' is an anagram indicator (I've seen this in other clues).
'eel' anagrammed gives 'ele'.
'ad'+'ele'='ADELE'
'the' acts as a link.
(Other definitions for adele that I've seen before include "girl" , "Popular female singer" , "Performer" , "Woman" , "Female English singer-songwriter, b. 1988" .)