Greene, who was given up for adoption on the day she was born in 1948, tried to send letters to her birth mother through her adoption agency, but the woman did not want contact.
Then, in 1987, a private investigator revealed who the woman was and where she worked. Greene decided to take an unusual approach to establishing a connection.
"I went to her office and pretended to be a flower delivery person," Greene, 67, tells PEOPLE. "When I handed her the flowers, I touched her on the shoulder and looked in her eyes and told her to have a nice day. Then I turned around and walked out."
Along with the flowers, Greene – a retired librarian who now lives in Crawfordville, Florida – included a card with a deeply personal message.
Courtesy Abbie Greene
The card read: "I just wanted to look in your eyes and touch you one time. I hope one day you'll want to chat with me. Love, your daughter."
The message worked. Greene was in tears in her car when her mother came out to find her and agreed to have lunch with her the following day.
While at lunch, Greene was bursting with questions she felt too afraid to ask. "We talked about cats and books and just everyday type stuff," she recalls. "We never got into the important stuff – I was afraid she'd disappear."
Greene and her mother continued to meet for lunch for years on the condition that Greene never share her mother's identity with anyone. Each time they met, the pair always had the same sort of everyday conversations and somehow, that felt like enough. "I was just so glad to be sitting across from her," Greene says.
An Extraordinary Discovery
In 2011, Greene joined the personal genomics website 23andMe in the hopes of finding her biological father. But instead, she found a sister.
In 2014, Greene made a "close family match" on the site with 50-year-old Liz Kellner, who had been left in a Minneapolis apartment building laundry room in a cardboard box when she was an infant. One year later, another sister appeared, this time on Ancestry.com. Tammy Makram was also abandoned in a cardboard box at just a few days old at a hospital in St. Paul, Minnesota.
Courtesy Liz Kellner & Tammy Makram
Last October, the three sisters came together for the first time for a special reunion with friends and adoptive families in Minneapolis, Minnesota. "There was an overwhelming feeling of love and connection between us," Makram recalls. Still, there was one person missing – the women's biological mother.
With Greene still sworn to secrecy over their mother's identity, Kellner, a former researcher, was left to track the woman down on her own. She eventually reached her biological father, who is married to her biological mother. When Kellner called to introduce herself, he threw a wrench into her carefully crafted plan.
"My birth father just kind of laughed and was like, 'Really?' and then he said, 'Here, do you want to talk to your mother?' " Kellner recalls. "As I was saying 'no' he handed her the phone and she said, 'No, I don't have any daughters and I didn't have kids and I don't know what you're talking about.' "
So, Kellner suggested that she and her sisters send their birth mother a bouquet of flowers on Mother's Day simply thanking her for bringing them into the world – and then giving them up.
Courtesy Liz Kellner & Tammy Makram
"I wanted to send something to her to say thank you for doing the right thing," Kellner says. "She gave us up. She didn't throw us in a dumpster, I was put somewhere safe, she gave Abbie up in a proper manner (through an adoption agency) and whether the situation she was in was bad or good is irrelevant. In that moment, she made the right decision for us and that had to be hard."
The day the bouquet was delivered, Kellner got a response.
"She called me and said that she did indeed have children and she said she was sorry and she actually thanked me for lifting a burden that she had held for 68 years," she says.
A Question Unanswered
After Kellner and Makram met, they took a road trip together to meet their biological parents. It was the first time the two women would have the chance to ask the one question on their minds: Why did their mother abandon them?
Kellner, who describes herself as the "more direct, less touchy feely" one of the two sisters was the one to ask the question. However, the answer didn't come.
"Because they are old, our mother does have some dementia and has kept this secret for almost 70 years, it's hard to tell what is repressed versus what is dementia versus 'There's no way in hell I'm going to talk about this,' " Kellner says.
"I think part of the reason she's so quiet is because of all the guilt and shame that came with all of this that she's carried for all this time," Makram adds. "I think she has to understand that we are thankful that we were given up for adoption, but we also want to get to know her."
Even though the two sisters may never get the answers to their questions, they've found plenty of comfort from the rest of their family.
"I grew up knowing that my mother, the person who should want you more than anyone, didn't want me," Kellner says. "And that, as it turns out, sticks in your head. So to now know the story and see all these people who want me in their lives – it makes me much more okay with who I am."
Courtesy Liz Kellner
The sisters talk every day and are planning to bring their families together for a big trip in the spring. In the meantime, they want to inspire others facing the same difficult choice their biological mother faced.
"We want to make sure people know that there are these safe haven programs where you can leave the baby if you do end up in a situation where you can't go through the proper adoption channels and you are scared," Kellner says. "When we were left, we are fortunate that we were put somewhere safe and we want to make sure that those systems remain in place."