Sorcha’s sister is holding frame (7)
I believe the answer is:
chassis
'frame' is the definition.
(base frame of a vehicle)
'sorcha's sister is holding' is the wordplay.
'is holding' says the answer is hidden in the clue.
'CHASSIS' is hidden in the letters of 'sorchas sister'.
(Other definitions for chassis that I've seen before include "Vehicle's base frame" , "Vehicle's structure" , "Vehicle structure" , "Vehicle's structural frame" , "Car body" .)