Fine Gael Senator Catherine Noone blamed tiredness from campaigning for her description of Leo Varadkar as autistic - and told supporters she believed the controversy was "already passing over".
As she battles to save her political career this weekend, Ms Noone has also told the Sunday Independent that she insulted people with autism "unintentionally".
This newspaper has seen an email to a parent who has a child with additional needs in which Ms Noone wrote: "The only possible explanation is that I was tired from campaigning.
"It was a throw-away comment that I shouldn't have made. I feel terrible."
In a separate apology in a WhatsApp group of her supporters, the Dublin Bay North candidate said: "I'm so very sorry for the comments I made so carelessly and everything that has ensued.
"I will make it up to you all in the coming days."
In her message to the 'Campaign For Catherine' group the day after her comments were reported by The Times, Ms Noone thanked her supporters for their "support and kindness" and shared an email from a constituent urging her to work with autism awareness campaigners.
These include Adam Harris, brother of Health Minister Simon Harris who is the founder and chief executive of AsIAm, Ireland's national Autism charity.
"Please God this is already passing over," Ms Noone said.
However, she faced an immediate backlash after posting the message with one long-time Fine Gael member responding: "Before I say something not nice please remove my details from your WhatsApp. I'm beyond disappointed."
Speaking to the Sunday Independent's Barry Egan about her controversial comments in the newspaper's Living section today, Ms Noone said: "Honestly, I just insulted people with autism unintentionally."
The parent who received the email from Ms Noone, Seanie Vaughan, said her response was "totally unacceptable" and that she should withdraw from politics.
"She is not the person you want as an elected representative," he said.
Despite being backed by Mr Varadkar and Fine Gael, who have accepted her apology, there are growing doubts about Ms Noone's future.
She is unlikely to take a Dail seat in Dublin Bay North, while the organisation that nominated the two-term senator to run for the Seanad four years ago has refused to say if it will do so again.
"The board have not yet made a decision and are meeting next month to discuss," the Irish Country Houses and Restaurants Association said.
Ms Noone did not respond to requests for further comment this weekend.
She became embroiled in controversy last Tuesday after The Times recorded her describing the Taoiseach as "autistic" while discussing his performance during the first TV debate of the campaign.
"He's autistic like, he's on the spectrum, there's no doubt about it," she said while canvassing in the constituency.
"He's uncomfortable socially and he doesn't always get the in-between bits."
Ms Noone subsequently denied using the word "autistic" and then said she did not mean it literally.
She gave examples of potentially offensive words that could be used out of context, including "special" and "n***er". She then clarified that she would never use the n-word, and said it was a bad example.
In a statement via the Fine Gael press office on the day her comments were reported, Ms Noone apologised "unequivocally" and withdrew all of her remarks, describing them as "completely unacceptable".
She was denied an opportunity to take part in broadcast interviews to explain herself after she did a mock interview with the Fine Gael press office.
Following discussions with the Taoiseach, Finance Minister Paschal Donohoe, who is Fine Gael's director of elections, and the party's general secretary, Tom Curran, Ms Noone has reached out to autism awareness organisations to apologise in recent days.
She spoke to Adam Harris by phone, and a spokesman for AsIAm said her "profuse apology" had been accepted.
Mr Varadkar said Ms Noone's apology was "good enough for me", but urged her to learn more about autism.
Amid confusion over Fine Gael's vote management strategy in Dublin Bay North last week, the local party organisation is understood to have resumed a letter drop in the constituency yesterday.
The letters urge voters in certain areas to give their first preference to Ms Noone and their number two to Richard Bruton, the sitting Fine Gael TD and Communications Minister, in a bid to maximise the party's vote and chance of taking two seats.