The idiot dumping child for her (5)
I believe the answer is:
'her' is the definition.
'the idiot dumping child' is the wordplay.
'HEIDI' is hidden within the letters.
But, I am uncertain how this is indicated.
'for' is the link.
Can you help me to learn more?
(Other definitions for heidi that I've seen before include "German lady's name" , "lady - from Cologne?" , "Girl's name (from German)" , "Novel Swiss girl" , "book" .)