That woman concealing yen quietly becomes over-excited (5)
I believe the answer is:
hyper
'over-excited' is the definition.
(I've seen this before)
'that woman concealing yen quietly' is the wordplay.
'that woman' becomes 'her' (I've seen this before**).
'concealing' means one lot of letters goes inside another.
'yen' becomes 'y'.
'quietly' becomes 'p' (p for piano and quiet).
'y'+'p'='yp'
'her' enclosing 'yp' is 'HYPER'.
'becomes' is the link.
(Other definitions for hyper that I've seen before include "Over-stimulated" , "Abnormally active" , "Unusually energetic" , "Really excited" , "extraordinarily energetic" .)