GLASGOW, Scotland (CNN) -

In November of last year, 19-year-old Aqsa Mahmood gave her father, Muzaffar, a long hug goodbye. He remembers, he says, because she looked especially beautiful. He remarked upon it to his wife, saying there was something different about his daughter.

The night before, she had asked her sisters to sleep together in one big bed. Aqsa gave a lingering farewell to her bedridden grandmother, and that's when Khalida, her mother, knew something was wrong.

Standing in her daughter's empty bedroom, Khalida told CNN, "There was something about the way she said 'Khuda Hafiz' (God's Blessings) while taking leave that day, which made us all wonder. My husband even asked if everything was OK, and I said she is fine."

Four days later, Aqsa called her parents back in Scotland, just as she was crossing into Syria from its border with Turkey. Her parents were left heartbroken and confused.

Her father says when he spoke to her about coming home, she said that she would see her family on Judgment Day and would like to be a martyr.

She has been prolific on social media, advocating ISIS and Islamic caliphate beliefs, and calling for attacks to be carried out in Western countries. She posts photos of AK-47s and exults in ISIS executions. Her recent posting online has called to follow the example set by "brothers from Woolwich, Texas, and Boston."

Family lawyer Aamer Anwar talked about the family's heartbreak.

"There was nothing they (Aqsa's parents) could have done different. She was a bedroom radical. And if this could happen to Aqsa, who had all the life chances, the best education that money can buy, a family that was moderate, liberal ... if it could happen to her, somebody who was so intelligent, then it could happen to any family," Anwar said.

Aqsa is said to be influenced by watching sermons online and coming in contact with people through social media that helped her make the trek from Glasgow to Syria.

Living the dream in Scotland

The Mahmood family was, in many ways, living the dream of many immigrants. Muzaffar moved to Glasgow from Pakistan in the 1970s. He was the first Pakistani cricket player for Scotland. He and Khalida bought a home in an affluent neighborhood and had four children. They went to the prestigious private school Craigholme down the road.

"She was the best daughter you could have. We just don't know what happened to her. She loved school. She was very friendly. I have never shouted at her all my life, all my life," Muzaffar laments.

Her parents insist there were no signs that the Glasgow teenager harbored any extremist beliefs.

She listened to Coldplay and read "Harry Potter" books. On her desk, colorful loom bands and bracelets hung from a goosenecked lamp, a dog-eared copy of "The Hunger Games" nearby.

But when the civil war in Syria flared, Aqsa grew increasingly concerned about the violence. She grew more religious, praying and reading the Quran. And when she went to her university, she gave up her music and childhood fiction. But her parents did not suspect anything extreme.

"She didn't go out much. Just with her sisters, she would go out to watch movies and go out eating. We all went together," Muzaffar says.

Her family was stunned when they learned she was headed for the rebel-held territory of Aleppo in northern Syria. Khalida says her daughter was afraid of the dark and didn't even know what bus to take downtown, much less how to cross the border into Syria.

'I don't know when she became this brave'

"She didn't like shouting. I don't know when she became this brave. She was scared to talk, scared to fly, and this is a very big step -- her flying to Syria. I can't believe this," Khalida tearfully says, explaining the shock the family feels about her daughter's decision.

"I know she is my daughter, but I feel that she is my friend. But she made one mistake, but otherwise, she is really a very good girl. Sometimes I am angry."

Her family describes her as a loving daughter who brought her mother tea in bed, helped massage her mum's tired feet and often assisted her handicapped grandmother. Her mother says Aqsa never complained despite being asked to help with housework.

Soon after her arrival in Syria, Aqsa told her family that she would marry.

Her father said she sent a message saying: "That's the process here. They don't let a girl stay alone. Now we have to find a mahram (male guardian). We have to get married here. Don't worry. I'll be OK. My heart is good."

But her parents, still worried, attempted to dissuade her.

"We used to tell her ... this is not Islam, some of these groups are not Islam. They are doing wrong things which we don't approve of. Obviously, no Muslim approves this."