Girl leading a festive event (4)
I believe the answer is:
gala
'festive event' is the definition.
(I've seen this before)
'girl leading a' is the wordplay.
'girl' becomes 'gal' ().
'leading' says to put letters next to each other (some letters go in front of others).
'gal'+'a'='GALA'
(Other definitions for gala that I've seen before include "Special sports event" , "sporting event" , "A show of charity" , "field day" , "Festive celebration" .)