The Senate's internal economy committee had given Wallin 30 days to repay the money following the committee's review of an audit into her travel expenses by the independent accounting firm Deloitte. That deadline would have been Monday, Sept. 16.
But in a statement issued Friday, the Saskatchewan senator says she fundamentally disagrees with the methods employed by the auditors in finding her expenses were ineligible, and says she made the expense claims in "good faith."
And Wallin says she will not resign as a senator.
"I wish to make it clear. I was not treated fairly by the Deloitte review, which was not conducted in accordance with generally accepted accounting principle, nor have I been treated fairly by the Senate committee. Evidence that casts doubt on the correctness of the amounts owing was either ignored or disregarded during the review," Wallin says in the statement.
"When I submitted expense claims, I did so in good faith, honestly believing that the reimbursement was appropriate. If mistakes were made, I am responsible for those, but there was never a deliberate attempt to thwart the travel policy that was in place at the time the claims were submitted," she says.
But Wallin saves her harshest words for her Senate colleagues on the internal economy committee.
"Unfortunately, the Senate committee succumbed to a 'lynch mob' mentality. There was no regard to procedural or substantive fairness. I am disappointed and angry about the way in which this matter was handled, and any implication that I behaved dishonestly," Wallin says.
The committee referred its report into Wallin's expense audit to the RCMP, which has not said whether it is investigating Wallin. Nonetheless, she said in her statement she welcomes "an independent and objective review by the RCMP" and says she will co-operate with any investigation.
"I have not done anything wrong. I am not guilty of any misconduct. Accordingly I will not resign as a senator. I will continue to act for the people of Saskatchewan and Canada, fulfilling the duties of a senator that have been entrusted to me," her statement says.
As the CBC's Greg Weston first reported this week, Wallin put her condo in New York City up for sale last month.