Granny seen in Dickens a godsend (7)
I believe the answer is:
bonanza
'godsend' is the definition.
(thesaurus)
'granny seen in dickens a' is the wordplay.
'granny' becomes 'nan'.
'seen in' indicates putting letters inside.
'dickens' becomes 'boz' (I've seen this in another clue).
'nan' going within 'boz' is 'bonanz'.
'bonanz'+'a'='BONANZA'
(Other definitions for bonanza that I've seen before include "Spectacular windfall" , "A striking example" , "Source of good luck or wealth" , "old cowboy series on TV" , "Source of sudden wealth, windfall (7)" .)