A woman's mothering heart (3)
I believe the answer is:
her
'a woman's' is the definition.
'mothering heart' is the wordplay.
'heart' says to take the centre.
The middle letters of 'mothering' are 'HER'.
(Other definitions for her that I've seen before include "Pronoun used of ship" , "Belonging to the woman" , "In the Midlands she" , "The woman's" , "Belonging to a female" .)