After reaching her goal weight she continued to purge and "restrict" nourishment, sometimes consuming no more in a day than a granola bar.
"Are you eating?" her mother would ask. "Yeah, yeah," she'd reply.
It was a disastrous course that could have ended with a fatal heart attack had the Washington Township teenager's mother not taken her for an unrelated physical exam in April. When Shannon came back for follow-up a week later, her doctor was shocked to discover the 5-foot-1 girl had lost 10 pounds.
Shannon was anorexic, the doctor said, and needed immediate intervention.
"I broke down," Shannon recalled. "I said, 'Mom, I never intended it to get this far.' "
They drove directly to Kennedy University Hospital's crisis center in Cherry Hill, only to learn that eating disorders need specialized treatment and that their options in South Jersey were limited.
The closest residential facility for the disorders on their side of the Delaware River was University Medical Center of Princeton, more than 60 miles from the Mahers' home.
Philadelphia and the Pennsylvania suburbs are home to three hospitals with established residential programs, typically with 30-day stays: the Belmont Center for Comprehensive Treatment in Philadelphia, Brandywine Hospital in Coatesville, and the Renfrew Center in Roxborough, which treats only women.
But Shannon's anorexia nervosa (radical weight loss through self-starvation) and bulimia (weight loss through vomiting or laxatives) had been diagnosed early, making her a candidate for intensive day treatment.
After much research, Shannon's parents discovered that Renfrew, the nation's first hospital devoted to eating disorders, had months earlier opened a day clinic in Mount Laurel, and enrolled her.
Shannon was terrified: "I thought it meant going to a mental hospital."
She pouted on the 45-minute drives, shared little with the clinic's psychologists and psychiatrist, and scowled at fellow patients in group counseling.
"It was torture at first," she said recently, sitting on a sofa at the clinic. "I didn't want to get rid of my eating disorder. I felt I was in control and could do whatever I wanted."
At the request of her counselors at Renfrew, where she concluded eight weeks of outpatient treatment in June, she did not divulge what she weighed when she began treatment.
Such numbers can give other anorexics and bulimics a dangerous goal, said Holly Grishkat, an assistant vice president for the chain of eating-disorder clinics.
Untreated anorexia and bulimia can lead to suicide or fatal heart attacks, said Sam Menaged, 64, a health-care lawyer who founded Renfrew in 1985. "And it's the most difficult psychological diagnosis to treat," he said.
"But it's never about the food - it's about control. Say you have peer pressure, or a death in the family, or your parents are always fighting, or there's abuse, which happens a lot. When life is out of control, the one thing you can control is food," Menaged said.
Recovery involves intensive group therapy, private and family counseling, nutrition and diet planning, and may include medicines, such as antidepressants.
Day programs generally last eight to 10 weeks and are often favored by health insurers because they are less costly. Grishkat, who manages several of Renfrew's 11 outpatient clinics, said the chain chose its Mount Laurel site because many of Renfrew's residential patients who live in South Jersey needed a transitional program to come home to.
"People don't like to cross the bridge," she said.
Other established day programs for eating disorders in South Jersey include the Temenos Center in Moorestown, the Eating Disorders Treatment Center in Marlton, and the University Medical Center of Princeton in Plainsboro.
For the first two weeks of her day treatment, Shannon refused to engage with her fellow patients. Then, one day, while waiting for lunch, she struck up a conversation with two of them, ages 17 and 25.
"For once in my life it was like someone was feeling what I was feeling," she said. They became close friends, "talking and joking" with Shannon in group therapy, where she began to open up.
Days later, in a private session, "I suddenly began to sob uncontrollably," Shannon says. With her counselor's arm around her shoulders, "I finally let go. It felt so good to let it all out."
"It" was the feeling of "self-hatred, suicide, and wanting to be gone" that had consumed her since eighth grade, when she began comparing herself unfavorably to thin girls at school and a slim older sister.
"I had never talked about [the self-hatred] with anybody. It was the greatest day of my life."
But epiphanies do not always transform behavior. Four weeks into treatment, Shannon had not abandoned her destructive habits even after stepping down to half-day, thrice-weekly sessions - until a counselor "got all in my face. She knew."
Shannon confessed she still was "using symptoms" - lingo for purging or restricting.
And with that came a transforming realization: "I'm not getting better if I'm going home and doing the same thing."
For the first time in seven months, "I had control over that voice in my head, telling me I had to purge."
In the six months since, Shannon said, she has stuck to her clinic-designed meal plan and sees a therapist weekly.
"It's not even an issue anymore," she said. "I'm in control of my life, my relationships, my schoolwork, and what goes into my body."
Contact David O'Reilly at 856-779-3841 or firstname.lastname@example.org.