She brought an application seeking documents against the organisation, which she described as a pseudo religious cult.
Ms Johnston claimed the documents were necessary in her action for damages against the church and three of its members - John Keane, Tom Cunningham and Gerard Ryan.
She alleged that while undergoing "treatment" offered by the church she suffered increasingly with a dissociative stress reaction, became intolerant and rejected family and friends.
Ms Johnston claimed she suffered a distinct personality change, would often adopt a fixed stare and simulated smile while switching off her feelings.
She also said she became increasingly confused and her health suffered.
The church and its three named members deny Ms Johnston's allegations. The organisation makes a claim of "sacredotal privilege" in relation to a "counselling" folder sought by Ms Johnston.
She alleged that at a time when to Mr Cunningham's knowledge she was in an "emotionally liable condition", he said courses known as "dianetic auditing" would greatly improve her sense of well-being. Pressure was exerted on her to have a test which took place in March 1992 and the evaluator was Mr Keane. Ms Johnston claimed Mr Keane and Mr Cunningham pressurised her into subscribing for a "purification rundown and training routing" at a cost of £1,200.
She was told to attend a "doctor" of the organisation who transpired not to be a registered medical practitioner but a cult member. She said she was persuaded to join the "Sea Organisation" and sign "a billion-year contract" to work for Scientology.
David O'Neill BL, for the church, said his clients believed they would suffer damnation if they disclosed the counselling folder.