Ms McCarty told the authority that she did not receive any parental leave payments during this time, but thought as she had sent her application through to the IRD she would eventually receive payments and assumed they must have been late, the authority said.
Ms McCarty said she did not follow it up until she returned to work because she owed tax and was not in the "frame of mind", having just given birth, the authority said.
About a year after returning to work, in September 2014, Ms McCarty made inquiries about her parental leave payments and was informed the IRD had never received her application.
Ms McCarty made a fresh application in October 2014, which was referred to the Ministry of Business, Innovation and Employment (MBIE).
The application was declined as it was made after Ms McCarty returned to work, the authority said.
MBIE said delays in filing her application were "excessive and unreasonable" as Ms McCarty had not made any inquiries with the IRD about her application.
Authority member Anna Fitzgibbon agreed, and said she did not accept Ms McCarty's reasons for failing to take necessary steps sooner to establish why she had not been paid.
"Ms McCarty made assumptions about why she had not received the payments from Inland Revenue Department and chose not to follow up. These delays in doing so were excessive and unreasonable.
"I therefore confirm the MBIE's decision that Ms McCarty is not eligible for paid parental leave."
There was no order on costs.
Both Ms McCarty and MBIE were being sought for comment.