Angela Kerins has lost her High Court action against the Public Accounts Committee.
The former CEO of the Rehab Group claimed its members acted beyond their powers during a PAC hearing she attended in 2014.
By asking about her €240,000 salary and bonus payments, she claimed the members acted outside their powers in what she described as a “witchhunt”.
The court heard previously that she was so overwhelmed by what happened that she later tried to take her own life.
In ruling against her, President of the High Court Mr Justice Peter Kelly said that the utterances complained of were clearly expressions of opinion devoid of any legal force.
He said she seeks to make the Oireachtas members amendable to the jurisdiction of the court – something that cannot be done.
To constrain members in the manner suggested would impair the effective functioning of parliament, he said, in a manner expressly forbidden by the Constitution.
In a statement Thursday evening, Ms Kerins said: "I am very disappointed in the decision of the High Court today.
"I would like to first thank those closest to me, my family, my friends and my highly professional legal team for their unrelenting support and guidance.
"It was an enormous decision to take this case and I could not have done it without them.
"I would also like to take this opportunity to thank the many people, those who I know and those who I do not know, who wrote letters to me, e-mailed me, text me, came up to me in supermarkets, cafes, on the streets and in many other places to give their support throughout this very difficult time.
"Their kindness and compassion is at the core of who we are as a nation and I thank them from the bottom of my heart.
"I am currently reviewing the written judgement of the High Court with my legal advisors.
"I will not be making any decision or making any further comment in this matter until that review is complete."