Former deputy speaker Anne Tolley expected Speaker Trevor Mallard's legal dispute to be costly when she agreed to tax payers footing the bill.
More than $300,000 from the public purse was spent in defamation proceedings after Speaker Trevor Mallard wrongly claimed an accused rapist was working on Parliament's premises.
Prime Minister Jacinda Ardern said Mallard's comments were a mistake, but he should remain in his role as speaker.
National has also called him to appear before a select committee on Wednesday to question him about the legal proceedings and money spent on them.
The party has claimed a rule change last year was used to benefit the speaker.
Tolley, a former National MP, changed the rules last year while she was deputy speaker so speakers, including Mallard, would have access to the same legal financial support as ministers.
She later signed off on the use of taxpayer money being used to cover Mallard's legal bill.
Tolley told RNZ Mallard made the comments as speaker and had no protection when legal action was taken against him.
There was then a discussion about whether the speaker should qualify for legal financial support as he was "essentially the minister of Parliamentary Services, he's responsible for the management of Parliament."
"It didn't seem right that there was not a similar protection for him," she told RNZ.
Tolley then received advice from a number of people, including the solicitor-general, and went on to develop a process similar to what is in place for ministers; the only difference being the deputy speaker has to sign off on the financial support instead of the attorney-general.
"I was surprised, in fact, that they didn't [qualify for legal financial support] so we set up a system whereby they did," Tolley told RNZ.
Before signing off on Mallard's case, Tolley said she received advice from Crown Law that indicated, roughly, how much it would cost the taxpayer.
"Because it was coming to the end of the Parliamentary term, the suggestion was that if it was within that envelope that Crown Law thought was reasonable that it be settled, and I signed off on that.
"I didn't have an exact amount but I did have a range of costs."
Tolley could not remember the exact range of costs she was given, but said the final $333,000 legal bill was within it.
When asked by RNZ if, in hindsight, she was happy with her decision to sign off on spending taxpayer money on the defamation proceedings Tolley said she was comfortable with it and that it was appropriate.
"The decision I made was to put in place a process that gave the speaker of Parliament the same protections as a Cabinet minister.
"The question of the rights or wrongs of any of the actions is a completely different question and you can only take advice on that from Crown Law."
As deputy speaker, Tolley said she set up a process that would protect all speakers of Parliament.
"At some stage National will be in government and they will have a speaker. We're a much more litigious community these days, so it may well be that National's speaker gets into trouble."
She would not comment when asked about National's criticism of the Speaker and the cost of the defamation proceedings on the taxpayer, but said legal proceedings were typically very expensive.