Jill Perkins showed "no remorse" about telling an ex-colleague about a "disparaging" letter about her boss, employment tribunal judge Kendrick Horne said.
The 66-year-old had a "complete lack of understanding that she had done anything wrong" when she emailed her former co-worker Sally Wright to tell her about the "wonderfully truthful" anonymous letter sent to the PDSA in Telford, Mr Horne said.
Mrs Perkins worked at the company's head office in Priorslee as a senior assistant to the director general's office.
But the tribunal judge also ruled that Mrs Perkins, of Randlay in Telford, should have been given six weeks notice, rather than dismissed immediately in July last year.
The hearing, at Telford Magistrates Court yesterday, had already heard the email included claims of bullying and harassment being rife and alleged that morale was low among staff at the organisation – as well as personally criticising director general Jan McLoughlin.
Mr Horne said the dismissal was fair because Mrs Perkins' position required a "high standard of professionalism, tact and absolute discretion" and the 66-year-old had shown "no understanding" that she did anything wrong by revealing the existence of the email.
Mr Horne said: "Had the complainant shown some understanding of her error of judgement and realised she had overstepped the mark it would have been utterly inappropriate to dismiss her."
He added: "It was within the range of reasonable responses to dismiss her therefore the dismissal was fair."
The emails, he said, did not break the trust and confidence between the employee and employer and ruled the PDSA and the respondent was not entitled to terminate her contract without notice.
He awarded Mrs Perkins damaged of £2,401.69, the equivalent of six weeks pay.
After the decision, Mrs Perkins, who said she planned to appeal, said: "I am devastated at what seems to be a total travesty of justice and truth. To have my exemplary career of some 46 years end on this shocking note is heartbreaking."
A PDSA spokesman said: "While it is disappointing that this case went to an independent employment tribunal, we are satisfied with the outcome, which fully supports our decision to dismiss a former employee."