A lady's case for agreement (7)
I believe the answer is:
compact
This clue is a double definition.
'a lady's case' is the first definition.
(compact mirror)
'for agreement' is the second definition.
(compact can mean an agreement)
(Other definitions for compact that I've seen before include "Dense; formal contract" , "Little" , "Mutual agreement" , "What comes initially with CD" , "it could be in the bag" .)