She has a line in stewed eels (5)
I believe the answer is:
elsie
'she' is the definition.
'has a line in stewed eels' is the wordplay.
'has a line' becomes 'i' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'in' is an insertion indicator.
'stewed' indicates an anagram.
'eels' is an anagram of 'else'.
'i' placed into 'else' is 'ELSIE'.
Can you help me to learn more?
(Other definitions for elsie that I've seen before include "Female name; rhymes with London football team" , "Lady" , "Girl's name" , "Name for girl" , "woman" .)