She gets in shape gradually (3)
I believe the answer is:
peg
'she' is the definition.
'in shape gradually' is the wordplay.
'in' indicates a hidden word.
'PEG' is hidden in the letters of 'shape gradually'.
'gets' acts as a link.
(Other definitions for peg that I've seen before include "that may have hat or coat on" , "Small cylindrical pin" , "This leg is artificial" , "Limit" , "Fix (a price)" .)