Demure actress has to respond (5)
I believe the answer is:
react
'to respond' is the definition.
(to react to something is to respond to it)
'demure actress has' is the wordplay.
'has' indicates the answer is hidden within the clue.
'REACT' can be found hidden inside 'demure actress'.
(Other definitions for react that I've seen before include "provide an answer" , "Perform again" , "Act as opponent" , "Show opposition" , "Respond to a stimulus" .)