Girl coming to harm following Jack (4)
I believe the answer is:
jill
'girl' is the definition.
'harm following jack' is the wordplay.
'harm' becomes 'i'll' (I've seen this before).
'following' is a charade indicator (letters next to each other).
'jack' becomes 'J' (playing card abbreviation).
'ill' after 'j' is 'JILL'.
'coming to' acts as a link.
(Other definitions for jill that I've seen before include "Female ferret" , "Jack's pet" , "Jack's nursery rhyme girl companion" .)