A couple of lines penned by each girl (4)
I believe the answer is:
ella
'girl' is the definition.
(girl's name)
'a couple of lines penned by each' is the wordplay.
'a couple of lines' becomes 'll' (two abbreviations for line).
'penned by' is an insertion indicator.
'each' becomes 'ea'.
'll' put inside 'ea' is 'ELLA'.
(Other definitions for ella that I've seen before include "- Wheeler Wilcox, US poet" , "Woman" , "Great late jazz singer . . . . Fitzgerald" , "- - Fitzgerald (mus.)" , ".... Fitzgerald, late great jazz diva" .)