American inventor's instinct about protecting little girl (6)
I believe the answer is:
edison
'american inventor's' is the definition.
(I've seen this before)
'instinct about protecting little girl' is the wordplay.
'instinct' becomes 'nose' (a nose for something is a good instinct for it).
'about' says the letters should be written backwards.
'protecting' indicates putting letters inside (inserted letters are held or protected).
'little girl' becomes 'Di' (short for Diane, Diana etc).
'nose' in reverse letter order is 'eson'.
'eson' enclosing 'di' is 'EDISON'.
(Other definitions for edison that I've seen before include "US scientist/inventor" , "Prolific inventor" , "Thomas Alva ......, great American inventor" , "Onside with great American inventor" , "scientist" .)