She tried an alternative being cast down (10)
I believe the answer is:
dishearten
'being cast down' is the definition.
(I've seen this before)
'she tried an alternative' is the wordplay.
'alternative' indicates anagramming the letters (an alternative ordering of the letters).
'she'+'tried'+'an'='shetriedan'
'shetriedan' anagrammed gives 'DISHEARTEN'.
(Other definitions for dishearten that I've seen before include "Take hope from" , "Bring down" , "dismay?" , "Put a damper on" , "cast down" .)