"The defendant has fraudulently performed this counter-initialling so as to be able to cash the cheques without the knowledge of other committee members," the police summary of facts stated.
On December 20, 2010 of the same year she used a social committee cheque to buy goods at Moore Wilson's to the value of $363.62.
"After the Christmas party on 2 December, 2010 there were no further social committee functions for the remainder of the year.
"For that reason it appears that this purchase was made by the defendant for personal reasons as opposed to reasons legitimately linked to the social club," it said.
She did not get a second member of the social committee to sign the cheque, as required.
Then on December 28, she again presented another cheque to Moore Wilson's to the value of $177.42.
On this cheque, she forged the signature of the counter-signatory.
In explaining to police what had happened, Bates said "it was probably for food and was possibly personal but she couldn't be sure."
"She couldn't be sure why a second signature wasn't sought or why the date was changed," police said in the summary of facts.
She admitted to police that it would "probably" have been her who forged the signature, but she was not sure.
She also told police that she recalled printing off two certificates, but not the remainder.
In Wellington District Court this morning, Bates pleaded guilty to all 13 charges.
Corrupt use of information and dishonestly using a document each carry a maximum sentence of seven years' imprisonment, and forgery carries a maximum sentence of 10 years' imprisonment.
Department of Internal Affairs spokesman Tony Wallace said it had auditing systems in place to catch employees accessing information they were not entitled to see and staff were subject to an information code of conduct.
"There are certain protocols that they've got to comply with around security, around appropriate use of computers - and that applies with access of information and usage, and the use of log-ins and passwords."
Bates will be sentenced on March 15.
She will be caring for her 15-year-old son, who has ADHD and Asperger's Syndrome, while he merges into mainstream schooling until sentencing.
Bates has indicated she would be seeking to complete restorative justice with the ministry.
Police would be seeking reparation, but a final figure had not been confirmed.