Author concealing her first twist (6)
I believe the answer is:
writhe
'twist' is the definition.
(I know that twist can be written as writhe)
'author concealing her first' is the wordplay.
'author' becomes 'write' (I've seen this before).
'concealing' means one lot of letters goes inside another (back).
'her first' becomes 'h' (wst letter of 'her').
'write' going around 'h' is 'WRITHE'.
(Other definitions for writhe that I've seen before include "Move sinuously" , "Twist in agony" , "Squirm in pain" , "6, maybe in agony" , "'Twist, squirm (6)'" .)