Yes indeed - a traitor to the lady (6)
I believe the answer is:
rather
'yes indeed' is the definition.
(I've seen this in another clue)
'a traitor to the lady' is the wordplay.
'a traitor' becomes 'rat' (rat can mean a treacherous person).
'to the lady' becomes 'her' (her refers to a woman).
'rat'+'her'='RATHER'
(Other definitions for rather that I've seen before include "Infinite time" , "with more justification" , "Yes, please!" , "To a limited degree" , "Quite; on the contrary" .)