A large beer, we're told, for old lady's-maid (7)
I believe the answer is:
abigail
'maid' is the definition.
(thesaurus)
'a large beer we're told' is the wordplay.
'large' becomes 'big' ('big' can be a synonym of 'large').
'beer' becomes 'ale' (I've seen this before).
'we're told' shows a homophone (sound like).
'ale' is a homophone of 'ail'.
'a'+'big'+'ail'='ABIGAIL'
'for old lady's' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for abigail that I've seen before include "Lady's maid (once); David's wife (I. Sam.)" , "She served David" , "Girl's name" , "Woman" , "Missing party girl" .)