"It was not me who was the complainant to ICAC. I knew nothing of the accident until I read of it in the press. She never asked me if I was responsible and I vehemently deny it," said Carol.

She was referring to the investigation by the Independent Commission Against Corruption into whether Margaret Cunneen advised her son's girlfriend to pretend to have problems with her breast implants to stop police doing a breath test at the scene of a car accident.

Carol Cunneen, 49, is now in an invidious position. She wants her sister to win her impending High Court battle against the ICAC.

But on the other hand, if Margaret does succeed and there is no ICAC inquiry, Carol says: "I will be the one seen to be vexatious, which I am not."

A fortnight ago Fairfax Media revealed that Margaret Cunneen, 55, had sent an email to a member of the public stating: "What a malevent [sic] person my long-estranged [family member] is to take the bare bones of the terrible crash that my father told her about and do this to me."

Carol Cunneen has confirmed she is the person to whom her sister was referring but she is adamant that she didn't know about the car accident until news broke of ICAC's investigation.

She said Margaret's claim she tipped off ICAC was ludicrous. "I am a clerk. Who would take my word over hers in anything?"

On October 30, 2014, ICAC issued a media release stating that on November 10 it would hold a public inquiry "into allegations that on 31 May 2014 Deputy Senior Crown Prosecutor, Margaret Cunneen SC and Stephen Wyllie, with the intention to pervert the course of justice, counselled Sophia Tilley to pretend to have chest pains, and that Sophia Tilley, with the intention to pervert the course of justice, did pretend to have chest pains, to prevent investigating police officers from obtaining evidence of Ms Tilley's blood alcohol level at the scene of a motor vehicle accident".

Margaret Cunneen took legal action to stop the public inquiry. After losing the first round of the legal battle, Ms Cunneen had a victory. On December 5 the NSW Court of Appeal ruled ICAC was acting outside its powers by investigating the well-known crown prosecutor.

Later that evening, Margaret Cunneen responded by email to a member of the public. In this email she not only blamed her sister for her woes but also said: "It is indeed amazing that these people don't realise that my dear Sophia doesn't drink (her blood test was 0.00) and the crash was so bad that the car was written off. Isn't it good that all the independent bystanders said I did absolutely nothing wrong?"

Carol has requested ICAC provide her with a statement saying she had no role in reporting Margaret to them. "I think that is only fair," she said.

She now finds herself over a barrel. She wants her sister to win the High Court battle because "she has done a lot of good for the community".

But if Margaret is successful she says she will be left appearing to be responsible for her sister's misfortune.

"I love all my family and we are all different people. But this is just a bit too much for me to accept," said Carol.

Margaret Cunneen did not return Fairfax Media's call.