But if JB was the perp he would know SC would not need roughing up because he wasn't roughed up.
That is correct. Neither Bamber or Sheila had any other injuries.
A badly injured Nevill was unable to inflict any injuries to Bamber.
Sheila provided no resistance. Therefore he did need to inflict any injuries to her.
Sheila providing no resistance also meant she inflicted no injuries to Bamber.