During the course of the appeal, it was discovered the BRC had been using fake names and signatures on the official versions of their decisions, which it said was to protect the identities of committee members.
The ministry argued the woman was one of a small number of clients on its "Remote Client Unit", considered to be a risk to staff, and therefore had to be dealt with more carefully.
However, the Social Security Appeals Authority said the use of fake names was an unlawful practice labelled "repugnant to the most fundamental concept of justice".
It said despite warnings - and a 2016 undertaking from chief executive Brendan Boyle that the practice of using false names during benefit review hearings would stop - it had not.
Boyle was found to have filed a further seven documents containing fake names and signatures since he was told not to, the authority said, which it condemned.
The Ministry of Social Development did not agree, and appealed that decision to the High Court. Yesterday, it lost the appeal.
Justice David Collins quashed any argument of staff members' health and safety being at risk by using their own names.
He said while Ms L's abusive and threatening communications were "unacceptable", the ministry had behaved unlawfully.
He ruled keeping the names secret breached Ms L's right to natural justice, as she would be unable to challenge the member's impartiality or their qualifications if she did not know who they were.
The ministry had received the decision and was considering it.
