Ken conceals a warm heart for her (5)
I believe the answer is:
karen
'her' is the definition.
'ken conceals a warm heart' is the wordplay.
'conceals' is an insertion indicator.
'heart' says to take the centre.
The central letters of 'warm' are 'ar'.
'ken' going around 'ar' is 'KAREN'.
'for' acts as a link.
(Other definitions for karen that I've seen before include "Girl's name - ethnic Thai in Burma" , "Girl" , "oriental language" , "One at home in 15 across [AARHUS]" , "Carpenter of note" .)