The next night, the two women crossed paths at the Rock Salt Bar and Restaurant in Kerikeri, where a fight broke out.
Both women claimed the other started it and both suffered injuries.
Ms Drader said the client struck her with a bottle, causing her face to become badly swollen.
She told the authority she got excitable and her husband had to persuade her to leave the bar.
Ms Drader laid a complaint with police that night, but did not contact her superior or have her injuries assessed by a doctor.
On Monday, she accessed the client's confidential records, taking down an unlisted phone number.
She phoned the client that night and allegedly threatened her, saying: "You better watch yourself, the dogs are after you."
It was not until Thursday that Ms Drader raised the fight with her immediate superior. She was suspended immediately.
At a formal meeting several days later, Ms Drader was told the client had laid a complaint. Confronted with the details, she admitted phoning and threatening the client.
The ministry raised a number of concerns with Ms Drader's conduct, including that she failed to notify her immediate superior of the fight for six days and accessed the client's confidential details in breach of the ministry's code of conduct.
She was sacked at a meeting the following month.
Authority member James Crichton found the ministry was justified in dismissing Ms Drader for serious misconduct.
"The errors of judgment of which she was found guilty, which she herself admitted to, were so fundamental as to make the loss of trust and confidence in her by the ministry a total one."
The ministry's inquiry into the matter was properly conducted and its decision to sack Ms Drader was the only available sanction given the "irretrievable breakdown in trust and confidence".
Costs were reserved.