Mistress Quickly's way to get fifty quid (4)
I believe the answer is:
nell
'mistress' is the definition.
'way to get fifty quid' is the wordplay.
'way' becomes 'n' (Compass direction - North).
'to get' is a charade indicator (letters next to each other).
'fifty quid' becomes 'ell' (I can't explain this - if you can you should believe this answer much more).
'n'+'ell'='NELL'
'quickly's' is the link.
This may not be right. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for nell that I've seen before include "Little -, (Dickens char.)" , "-- Gwyn, royal favourite" , "little Miss Trent?" , "Dickensian heroine" , "Little --; -- Gwyn" .)