"I considered myself part of a team, and I thought I would do the right thing — 'I'll pay this money back, and write this cheque,'" she told NewsTalk 1010 radio host Ryan Doyle, who is anchoring the show while regular host John Tory is on the Toronto municipal election hustings.
It was a decision she said she made "against advice from many people" — and one she now regrets.
"It's been used against me."
If she could do it all over again, she said, "I would pay back what I think I owed, but not the large sum of the charges that were rung up because of retroactively imposed new rules ... I just think it's given some people an excuse to say 'oh, well, you must be guilty because you paid it back."
In November 2012, Wallin initially paid back just under $40,000. A subsequent Senate audit found nearly $150,000 in potentially problematic expenses.
Wallin spent three hours in the Toronto radio station's guest host chair, where she found herself discussing everything from the pros and cons of walking kids to school to traffic congestion to her own ongoing trials and tribulations.
She told Doyle she's still not sure that she did anything wrong, although she acknowledged that "mistakes were made, no question about that — but not many."
"We have rule of law and due process and you should be given the chance to state your case," she said, but added that she felt that didn't happen.
"I walked into a meeting with board of internal economy and [my lawyer] wasn't allowed to speak. I couldn't make a case. The endless amount of information we presented was not considered."
She also stressed that the rules themselves were "subjective."
"What I can do on Tuesday, the guy down the hall can't do on Wednesday. Some of the rules are so vague — it's about interpretation."
The former TV news anchor — who told Doyle she felt like she was getting back to her journalistic roots — was also candid about the public reaction to the controversy.
"It's frustrating, particularly for someone who has spent most of her life in the information business," she said.
"But I found when I took the time to answer the email — and we got lots of hate email — that I would sit down and I would answer 10 or 15 emails, and say, perhaps you don't know how the system works and I'd like to give you some facts. I'd get emails back saying, oh right."
"There were literally thousands of Canadians who were very supportive, and said we know who you are, and we've heard you on this," she recalled.
"I found a lot people who were ready to give me the benefit of the doubt."
Wallin's file is currently one of several being reviewed by the RCMP, but she said she hasn't heard anything about the progress of that investigation.
Last week, the RCMP announced that it wouldn't lay charges against former PMO chief of staff Nigel Wright over the $90,000 payment he made to Senator Mike Duffy.
Retired former Liberal Senator Mac Harb and one-time Conservative turned Independent Senator Patrick Brazeau were charged with fraud and breach of trust in February.