Kenneth conceals a hard heart from her (5)
I believe the answer is:
karen
'her' is the definition.
'kenneth conceals a hard heart' is the wordplay.
'kenneth' becomes 'ken' (short for Kenneth).
'conceals' means one lot of letters goes inside another.
'heart' indicates the central letters.
The centre of 'hard' is 'ar'.
'ken' going around 'ar' is 'KAREN'.
'from' is the link.
(Other definitions for karen that I've seen before include "Girl's name - ethnic Thai in Burma" , "oriental language" , "One at home in 15 across [AARHUS]" , "Carpenter of note" , "Girl" .)