It breaks Mulligan's heart to think that the mystery woman, who said she wasn't from this area, may have been her long-lost sister.
"I'd have just stopped everything and snatched her up in my arms," she said. "I always wished I had a little sister."
Mulligan's mother kept the story hidden from everyone but her oldest daughter and her longtime boyfriend, the family said.
Dunahugh, 71, revealed the secret to Mulligan on her birthday Aug. 14. Mulligan had picked up her mother to go shopping that day.
"As soon as we got in the car she just blurted it out," Mulligan said. "I didn't believe her."
Later, Mulligan called her half-sister Sandra Fox, 50, in Santa Rosa, Calif., who confirmed the story.
Mulligan broke the news to her brother, Terry Brown, 37, of Hagerstown, and her three half brothers, Carlos Dunahugh, 46, of Boonsboro, Curtis Dunahugh, 43, of Smithsburg, and Brian Shoemaker, 31, of Hagerstown.
The siblings have mixed feelings.
"Everybody's a little confused, a little mixed up," said Curtis Dunahugh, a welder, who was 12 when the girl was born.
Their mother wasn't a small woman, making it relatively easy for her to hide the pregnancy. When she went to the hospital to have the baby, the children were told she had gone in for a tumor operation.
"I guess I'm curious. I just don't know how I feel about it," said Carlos Dunahugh, a civil engineer and technician.
"You grow up with certain absolutes in your mind," said Brown, an electronics technician.
But Brown and Mulligan knew right away that they wanted to find their sister, although their efforts have come up empty.
They entered their names in a Baltimore adoption registry in case she is looking for them.
They filed a petition to open the adoption record in Washington County Circuit Court.
They're also lobbying for a bill in the Maryland General Assembly that would open the adoption records of adoptees over 25.
Brown said he would like to tell his baby sister goofy family stories, like the time he cut Annette's hair when she was little.
"I just want to know if she's alive and what she looks like," said Mulligan, who works as a bartender at the Fireside Restaurant and Lounge. "I'd love to make a relationship, but if she doesn't want to, I understand."
The siblings said they understand their mother's decision to put the child up for adoption.
They were a poor family in the East End of Hagerstown.
Verna Dunahugh worked as a sewing machine operator at Dorbee Manufacturing Co. and E.J. Fennel Inc.
"She worked hard all her life," Mulligan said.
The boys always got new jeans and shoes at the beginning of each school year. Verna Dunahugh made most of Mulligan's clothes.
Although Verna Dunahugh doesn't talk much about the daughter she hasn't seen, her other children believe that she wants to know what happened to her. That's why she revealed her secret after all these years.
"She's worried how the girl's going to feel about her," Mulligan said. "I keep calling her the girl because I don't know her name. It feels weird."