Mary, her adoptive parent, and her birth mother, the woman she publicly refers to only as "Sarah."
In her just published-memoir "An Affair With My Mother," Palmer, a freelance journalist, has written an extraordinary tale not just of her search for her birth mother, but also of what she calls a legacy of secrecy and shame that has surrounded young unwed Catholic mothers in Ireland for decades -- and her own determination to break that cycle as a young mother herself.
"This book was a gift not just to Sarah but to my children," she said.
Palmer, 44, is one of thousands of Irish children who were born out of wedlock in an era when young unwed Catholic mothers were often forced by their families and the Catholic Church to give up their children in secrecy to avoid what their families saw as shame.
With an Irish lilt and the delicate walk of a dancer, Palmer gives no hint of the years of pain upon meeting her today. But she is ruthless in confronting it.
"The fact that I have been this object of shame has been the primary legacy of toxicity of this terrible secret," she said. "I am also a journalist, so my way of dealing with the pain was to investigate it."
The result is her new book, published earlier this year to acclaim in Ireland. She tells of the search for her mother and the secret relationship they developed.
In addition to informing the public by sharing her experience, she wants to make sure he own children know their family history, too, and don't feel it's something that must be hidden.
Her story has echoes in the movie "Philomena," in which Judi Dench plays an Irish woman who was forced to give up her baby for adoption as a young unwed mother and decades later tries to find him.
In Palmer's case, she knew from an early age that she was adopted.
"I was told I was adopted on my sixth birthday," Palmer related. "I was making my bed with my mother. At that moment she chose to tell me."
That alone was extraordinary in Ireland, where unwed mothers, secret adoptions and the role of Ireland's Catholic Church have remained national secrets. But Mary went a step further, telling her daughter to always remember her birth mother and say a prayer for her each birthday.
By 1999 at age 27, Palmer -- then working in Bosnia -- started the search for her birth mother. She was working for an aid group locating and identifying the war dead, all the while looking for her own birth mother.
The search for her was relatively short. The Catholic agency that brokered the adoption contacted Sarah and eventually the two met.
But that was only the beginning of an extraordinary relationship that would take a turn Palmer did not foresee.
For the decade after their meeting, the two women sent text messages and secretly met every time Palmer came to Ireland to visit her adoptive parents, Mary and Liam, the people she today firmly calls "my parents."
The meetings with Sarah in hotels around Ireland eventually included Palmer's husband and children.
Sarah, though, didn't tell her husband or children about the baby she gave up for adoption. But she told Palmer that she had never forgotten about her, often thinking of her late at night after the family went to bed.
"That is the rule of the affair we have been having because I am secret. Because she has never told anyone about me," she said about that period.
It was a joy to know her birth mother and painful to live with the limitations Sarah set for the daughter she long ago had to give up.
There were no phone calls, no letters, no emails. The only communication over the years was text messages.
Eventually, Sarah told two of her three children about Palmer and the siblings met: "They welcomed me into their life."
But to this day Sarah's husband and other child do not know the secret. Sarah was too afraid to tell the entire family.
Still, when Palmer told Sarah of her plans to write a book, she was supportive.
"Her words were always, 'Go for it, Caitriona.'" But even before the book was published earlier this year, something had changed.
October 2014 was the last time she saw Sarah. She never heard from her again after Christmas Day 2014.
Palmer believes Sarah may be "terrified" the rest of the family will learn of her secret. And while she describes the constant worry about Sarah and what may have sent her into silence, Palmer has found some solace in the hundreds of emails she has received since the book came out from other "secret mothers and secret children," all living for years in dreadful silence.
She has personally answered all of them.
Palmer expresses total and uncompromising compassion for Sarah. But she makes clear being the mother she wants to be is all-important.
She finds comfort in having rejected secrecy with her own three children.
"I have a wonderful life," she said earlier this week in Washington, where she and her husband eventually settled. "I have a wonderful husband and children."
On this Mother's Day, she is holding the past dear but very much living in the present.
"It was very important to me I break the generational cycle of secrecy," she said. "I wanted for my children to be able to let this out into the light."