One rogue tailing girl leaving early (7)
I believe the answer is:
initial
'early' is the definition.
(thesaurus)
'one rogue tailing girl leaving' is the wordplay.
'one' becomes 'i' (roman numeral).
'rogue' indicates anagramming the letters.
'girl' becomes 'g'.
'leaving' is a deletion indicator.
'tailing' with 'g' taken away is 'tailin'.
'tailin' is an anagram of 'nitial'.
'i'+'nitial'='INITIAL'
(Other definitions for initial that I've seen before include "Start of name" , "First home, corgi, ultimately, wagging tail" , "Name's first letter" , "First - opening" , "Introductory" .)