She solved one of those mysteries in late January and, on Thursday evening, met her long-lost brother, Thomas Linton, for the first time.
"Uh oh. He texted me he just landed," she said, her voice a mix of joy and anxiety. And then, there he was, a slim young man with a military buzz cut, big grin and searching blue eyes that remained fixed on Cook.
"Hey," he said, as brother and sister closed up the missing years with one big hug.
"Right when I was walking out, I couldn't help but smile," Linton said moments later.
Cook was just a year old when her mother gave birth to a second child, a boy, in 1990. Bobbi Ann Campbell kept the infant just two days before placing him for adoption, handing him directly to Kent and Helen Linton. Over the next four years, Campbell received letters and photos, sent through the agency that handled the placement, from her son's adoptive parents. They were perplexed when Campbell suddenly stopped picking up the letters, Helen Linton said, butthey kept writing for a time anyway.
"They didn't know her last name, so they didn't know anything had happened to her," said Cook.
On Dec. 27, 1994, Campbell, then 24, left her daughter with a friend while she went to the bank, grocery store and to pick up a paycheck from SOS Staffing Services in Salt Lake City. Campbell, who investigators say had drug problems, never picked up the check. She never came back for her daughter, either.
Cook, who was five, went to live with her great-grandparents; days later, the family filed a missing person report on Campbell.
For a time, it appears Campbell stayed in the Salt Lake City area. Investigators believe Campbell was spotted in a local park six months later. In the fall of 1995, her vehicle was found abandoned in front of a home near the Jordan River. Family found Campbell's makeup, purse and clothes inside the car along with Christmas presents from the previous year.
But there was no sign of Campbell, one of more than 50 people listed at Utah's Missing Persons Clearinghouse.
Cook grew up longing for her mother and wondering about her brother, whom she knew only through photos taken immediately after his birth.
"I always knew I had a brother but I didn't talk about it in our house," she said. "It was just confusing."
As a teen, Cook took over the task of spreading word about her mom, posting information on missing persons' websites and handing out fliers at Liberty Park, which she had visited often with her mother as a child. She also began searching for her brother, concentrating on Seattle because that locale was written on the back of his baby photos. She knew his name was "Thomas" and also had his parents' names.
But both efforts turned up nothing.
Then, in January, Cook jokingly told a co-worker who was moving to Seattle to keep an eye out for her brother. That got Cook thinking again. She sat down at a computer, pulled up Google and typed, "Thomas Salt Lake City adopted 1990."
Among the links that popped up: A 2010 newspaper story about a high school student named Thomas Linton who had won an award for pro-life activities at Juan Diego High School. In the article, Linton said he was trying to locate his birth parents, whom he knew only as "James" and "Bobbie."
"I couldn't talk. I was overwhelmed," said Cook. "It was too good to be true."
While Cook stepped away from her desk to calm herself, the coworker looked up the adoptive parents' telephone number.
"When I called and told them who I was, the first thing Kent said was, 'What happened to Bobbie?' " said Cook.
Helen Linton said the answer was a shock to them all, especially Thomas, who had never understood why his birth mother had stopped writing back.
On Jan. 30, Cook met Helen Linton and also spoke for the first time with her brother, a brief but emotionally overwhelming conversation.
In the weeks that followed, Cook and Linton who now lives in Selma, Ala., and is preparing to enter the Army have slowly gotten acquainted through telephone calls and daily text messages.
"The first few texts were, 'What's your favorite color? What music do you listen to? What was your life like growing up?' " she said.
The two exchanged photos of themselves they discovered they share the same nose and blue eyes and Cook sent her brother photos of their mother.
Now Linton wants to volunteer in any way he can to help find her.
He'll start by giving a DNA sample to use in identifying Campbell, if she is ever found.
"There is not very much we can do at this point," Cook said.
Except keep getting the word out.
On Friday, Cook will take Linton for his first visit to the memorial for their mother at Larkin Sunset Gardens cemetery in Sandy. They'll hold a small service and release a bouquet of balloons, sending their hopes for an answer to that final mystery skyward.
Bobbi Ann Campbell
Stephanie Cook and Thomas Linton will hold a public memorial for their mother, Bobbi Ann Campbell at 4:30 p.m. Friday at Larkin Sunset Garden cemetery, 1950 E. 10600 South, Sandy.
Campbell disappeared in 1994 and her family has not heard from her since.