Stress appeal is to be found in children’s book heroine (9)
I believe the answer is:
italicise
'stress' is the definition.
('stress'->'italicize' is in my internal thesaurus and 'ize'->'ise')
'appeal is to be found in children's book heroine' is the wordplay.
'appeal' becomes 'it' ('it' can mean something attractive or appealing).
'to be found in' indicates putting letters inside.
'children's book heroine' becomes 'Alice' (Alice's Adventures in Wonderland).
'is' going within 'alice' is 'alicise'.
'it'+'alicise'='ITALICISE'
(Other definitions for italicise that I've seen before include "Slant (writing)" , "How printers emphasise" , "make its characters right-leaning?" , "In email, make a big deal" , "Print in sloping letters" .)