Stony heart found in this girl (5)
I believe the answer is:
olive
'girl' is the definition.
(girl's name)
'stony heart found in this' is the wordplay.
'heart' indicates the central letters.
'found' says to put letters next to each other.
'in this' becomes 'live' (I can't explain this - if you can you should believe this answer much more).
The middle letter of 'stony' is 'o'.
'o'+'live'='OLIVE'
Can you help me to learn more?
(Other definitions for olive that I've seen before include "Female" , "Oil producer" , "Oily stone fruit" , "Cocktail fruit" , "It's branch is a symbol of peace" .)