Mistress in a chateau having friendly talk with girl (10)
I believe the answer is:
chatelaine
'mistress in a chateau' is the definition.
(historical term for a woman running a large house)
'friendly talk with girl' is the wordplay.
'friendly talk' becomes 'chat' (a chat is a casual conversation).
'with' is a charade indicator (letters next to each other).
'girl' becomes 'Elaine' (girl's name).
'chat'+'elaine'='CHATELAINE'
'having' acts as a link.
(Other definitions for chatelaine that I've seen before include "one looking after a big house" , "Woman running a household" , "formerly the mistress of a castle" , "Woman in charge of a large house" , "Mistress of the house" .)