Her diction suggest she's a Chelsea girl (5)
I believe the answer is:
elsie
'her' is the definition.
'diction suggest she's a chelsea girl' is the wordplay.
I cannot quite see how this works, but
'girl' could be 'elsi' and 'elsi' is found within the answer.
A single letter 'e' remains which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for elsie that I've seen before include "Name for girl" , "Girl's name" , "Female name; rhymes with London football team" , "woman" , "Lady" .)