Not really a mousy woman (5)
I believe the answer is:
shrew
'woman' is the definition.
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for shrew that I've seen before include "Mouselike insectivore" , "Scold, termagant" , "Mouse-like animal or scolding woman" , "Small mammal with a long snout" , "difficult woman" .)