Returning favour to Ms Darling perhaps, as compensation (6,5)
I believe the answer is:
saving grace
'compensation' is the definition.
(a quality which compensates for bad ones)
'returning favour to ms darling perhaps' is the wordplay.
'returning favour to' becomes 'saving'.
'ms darling perhaps' becomes 'Grace' (lighthouse keeper's daughter Grace Darling).
'saving'+'grace'='SAVING GRACE'
'as' acts as a link.
(Other definitions for saving grace that I've seen before include "Redeeming quality" , "Compensatory good point" , "What stops one condemning" , "Redeeming feature" , "a description of Miss Darling?" .)