Girl called on regularly (4)
I believe the answer is:
cleo
'girl' is the definition.
'called on regularly' is the wordplay.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
'called'+'on'='calledon'
The alternating letters of 'calledon' are 'CLEO'.
(Other definitions for cleo that I've seen before include "Dame Laine" , "She ruled" , "Woman" , "Carry on -- (1964 film)" , "Ms Laine - one of the 14 films" .)