But she will keep quiet for some reward! (5)
I believe the answer is:
shrew
'but she' is the definition.
I can't judge whether this definition defines the answer.
'keep quiet for some reward' is the wordplay.
'keep quiet' becomes 'sh' (as in shushing someone).
'for' means one lot of letters go next to another.
'some reward' becomes 'rew' (I can't justify this - if you can you should believe this answer much more).
'sh'+'rew'='SHREW'
'will' acts as a link.
Can you help me to learn more?
(Other definitions for shrew that I've seen before include "Small mammal with a long snout" , "insect eater" , "Mouse-like animal or scolding woman" , "Insectivorous mammal" , "Small mouselike animal" .)