(CNN) -- For 18 years, a girl who was whisked away into a secret backyard compound was forced to grow up in isolation.
Jaycee Lee Dugard was 11 years old when she was abducted and secreted away in a backyard compound.
By the time authorities discovered Jaycee Lee Dugard, she was a 29-year-old mother of two who had spent more than half of her life in sheds. One of the alleged abductors, Phillip Garrido, is the father of her two daughters, according to police.
Garrido and his wife, Nancy, face 29 felony counts, including kidnapping for sexual purposes, forcible rape and forcible lewd acts on a child. They pleaded not guilty Friday. The maximum penalty for each defendant, if convicted, is life imprisonment.
Dugard, who disappeared from South Lake Tahoe, California, in 1991, faces a challenging road to recovery. Dr. Kerry Landry, a child psychiatrist in Durham, North Carolina, said that repeated abuse causes complex trauma.
"They can really feel like they have no control and there is no escape," Landry said.
Aside from the physical abuse of children, experts say perpetrators find ways to manipulate the minds of the children they are abusing. Watch CNN's Brian Todd on challenges facing Jaycee Lee Dugard »
"Sexual abuse doesn't happen in silence," said Karen Duncan, a clinical therapist. "Things are said to the child before, during and after. Offenders say things in a purposeful way -- to convince the child what they're doing is OK and acceptable. The children do not know the laws. They really don't know this is something that's not supposed to happen."
Neither Landry nor Duncan are involved in the case but they agree that although the relationship over 18 years between Dugard and her alleged captors is still unclear the Garridos probably took psychological advantage of the child.
In sexual assault cases, adults threaten or lie to get children under their control.
"We don't know if she was told her parents didn't want her anymore, or that if she tried to escape, they would kill her parents," said Dr. Sharon Cooper, a developmental and forensic pediatrician, who also is a consultant for the National Center for Missing & Exploited Children. "There are many threats to compliance in these kinds of situations."
Because Dugard remained at the Garridos' compound for 18 years, she could have identified with her captives, experts said. Dugard may actually miss her captors now because they have been the center of her world for so long, forensic psychiatrist Helen Morrison told CNN.
"That was her life," Morrison said. "That's what she knew. That's the only thing she had. It's a little variant of what we call the Stockholm syndrome where you become identified with your kidnappers and in many ways, you become attached to them."
"The only reality she has is the life that she's lived. So she has to be overwhelmed," she said.
Stockholm Syndrome could be a survival mechanism for the victim, Landry said. "They try to form this relationship with their captor that will keep them alive and well, sometimes even though a part of them knows this is horrible and wrong," she said. "In order to survive and tolerate such a terrible situation, they essentially have to suppress that."
Dugard could face a long road to recovery as she familiarizes herself with the new world outside the Antioch, California, compound, experts said. Watch aerial view of backyard compound »
"It would be a little like being a time traveler, of being introduced to a world you have no concept of," Morrison told CNN. "You're going to be absolutely overwhelmed." In addition, she would have to deal with a change of identity -- she apparently was known as "Allissa" while living in the backyard compound.
"It's going to take a long time to build trust and be introduced to a world so foreign to her," said Duncan, a therapist who specializes in child sexual abuse and family violence. "She definitely needs the time to acclimate. Not only is her own recovery important, but for her own children as well. It would take several years."
Dugard's two daughters must also transition to a life they have never known, since they were born into the compound. The two girls, who are 11 and 15 years old, did not attend school or receive medical care, according to police.
Garrido told CNN affiliate KCRA-TV of Sacramento, California, that "those two girls slept in my arms every single night from birth; I never kissed them." Watch interview with Garrido »
The pivotal step for Dugard is to get connected with a mental health professional, Landry said. It's essential to reinforce to survivors that what happened is not their fault.
In 2002, Utah teenager Elizabeth Smart was kidnapped from her bedroom and held captive for nine months. The 15-year-old was reunited with her family in March 2003.
On Thursday, she told CNN's Anderson Cooper that after the reunion she spent lots of time with her family and advised survivors to not let "this horrible event take over and consume the rest of your life. Because we only have one life and it's a beautiful world out there."
"I would just encourage her to find different passions in life and continually push forward ... [and] not to look behind, because there's a lot out there," Smart said.
CNN's Taylor Gandossy, Tom Watkins and Stan Wilson contributed to this report.