Type of children’s book heroine mostly following it (6)
I believe the answer is:
italic
'type' is the definition.
(italic is a kind of type)
'children's book heroine mostly following it' is the wordplay.
'children's book heroine' becomes 'alice' (Alice's Adventures in Wonderland).
'mostly' means to remove the last letter.
'following' says to put letters next to each other.
'alice' with its last letter taken away is 'alic'.
'alic' put after 'it' is 'ITALIC'.
'of' acts as a link.
(Other definitions for italic that I've seen before include "Sloping type of print" , "Inclined to emphasise" , "Relating to slanting handwriting or type" , "more oblique than Roman" , "Group of languages" .)