The correct option is A As soon as she had realised her mistake, she started taking corrective action.
Option A is the correct sentence. It retains the meaning, and it is also grammatically correct.
‘As soon as’ is used as a conjunction of time. It means ‘immediately after.’
Other options change the meaning of the combined sentence.
Option B changes the sequence of events. They imply that first, she took the corrective action, and then she realized the mistake. It seems irrational and changes the original meaning of separate sentences.
Option C fails to tell the time gap between the corrective action and the realisation of the mistake. It gives a possibility that action might have come after the passing of some time that can be in days, months, or years. In the original sentence, the action was immediate after the realisation.