She's so loveless, the American one! (5)
I believe the answer is:
susan
'she's' is the definition.
'loveless the american one' is the wordplay.
'loveless' becomes 's' (I can't justify this - if you can you should give a lot more credence to this answer).
'the american' becomes 'us' (abbreviation for United States).
'one' becomes 'an' (I've seen this in other clues).
's'+'us'+'an'='SUSAN'
'so' is the link.
Can you help me to learn more?
(Other definitions for susan that I've seen before include "female" , "- - Sarandon (films)" , "Black-eyed -; lazy -" , "Girl's name, meaning lily" , "Girl (sometimes lazy?)" .)