Lamb, so-called, following American girl (6)
I believe the answer is:
amelia
'girl' is the definition.
'lamb so-called following american' is the wordplay.
I cannot quite see how this works, but
'lamb' could be 'elia' (pseudonym of essayist Charles Lamb) and 'elia' is found within the answer.
'american' could be 'am' (abbreviation in some contexts) and 'am' is found within the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for amelia that I've seen before include "-- Earhart, flyer" , "Fielding novel" , "Bloomer maybe" , "-- Earhart, US aviation pioneer" , "Legless condition" .)