Story about new girl's first knot (6)
I believe the answer is:
tangle
'knot' is the definition.
(I know that knot can be written as tangle)
'story about new girl's' is the wordplay.
'story' becomes 'tale' (synonyms).
'about' is an insertion indicator.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'girl' becomes 'g'.
'n'+'g'='ng'
'tale' enclosing 'ng' is 'TANGLE'.
'first' acts as a link.
(Other definitions for tangle that I've seen before include "'Twisted mess, muddle (6)'" , "Twist, snarl, knot" , "Trap < tall guy from Perth" , "A knotted mess" , "Enmesh, snarl up" .)