Girl exercising daily (5)
I believe the answer is:
lydia
'girl' is the definition.
(woman's name)
'exercising daily' is the wordplay.
'exercising' indicates an anagram (letters exercise or move around).
'daily' is an anagram of 'LYDIA'.
(Other definitions for lydia that I've seen before include "Old kingdom" , "lady" , "where Croesus was king" , "Old country" , "girl" .)