The family of a young Canadian woman who travelled to Syria after being radicalized say losing her was the most "shocking thing in the world" and that they wish CSIS had done more to prevent the 23-year-old’s departure.

The woman, whom CBC News is calling Aisha to protect her identity, made the journey to Syria to join up with ISIS last summer, after taking an online course to study the Qur’an taught by a woman based in Edmonton, says her older sister Rabia (whose name has also been changed).

"We all went to work, came home, all her stuff was gone. She had packed all her winter clothes, took her computer and left,” Rabia says.

"It was the most devastating, most scary, most shocking thing in the world."

Over the past several months, Rabia has been speaking to CBC News about her family's ordeal. Some details, such as names and the family’s location, are being withheld for security reasons.

The Canadian Security Intelligence Service declined to comment on the specific case, but said in an emailed statement that terrorism "including radicalization of Canadians and terrorist travel remains the most prominent threat to Canadian interests and our national security."

CBC Investigates

This family’s story is part of a CBC News investigation into extremism in Canada that shows young women in this country are not immune to the propaganda of ISIS.

If you have more information on this or related stories, email investigate@cbc.ca

Rabia alleges Aisha was recruited under the guise of an online class to study the Qur'an taught by a woman in Edmonton. But instead, Rabia says, Aisha learned how to get to the ISIS-controlled city of Raqqa in Syria.

CBC News has confirmed the identity of the woman in Edmonton and that she was asked to leave a mosque after she attempted to recruit people. She has not been charged in connection with this case.

Never coming home

When Aisha called home from abroad, she told her family she was never coming home — that Syria was where she was going to die.

The family had a moderate Muslim upbringing, Rabia says. Looking back, she says there were signs Aisha was changing. Aisha withdrew from her family and social circle, started wearing a niqab and retreated to her bedroom and computer, Rabia says.

Aisha also dropped out of college to study Islam full-time with the woman in Edmonton. The family believes it was that woman who paid for her plane ticket abroad, Rabia says.

CBC has not been able to independently confirm the details of Aisha’s radicalization or how she funded her travel, but it's known that she went to Edmonton, then Toronto. She flew to Barcelona and on to Turkey, where she crossed the border into Syria.

CSIS won’t comment on specific investigations, but Rabia says the agency had been tracking Aisha for nearly two years.

'I would have ripped her passport up'

Staff with the intelligence agency approached the family before Aisha left in the summer, but Rabia says they provided almost no information, aside from pointing out that Aisha’s Twitter account featured the ISIS flag and followed some prominent ISIS members.

"They told us she had been interacting with people they thought were dangerous and were influencing her in a negative way, but they didn't give us enough information and it was all very vague."

"If they had shown me the emails between my sister and this girl. If they had let me listen to the recordings of them planning on going places," Rabia says, it would have given the family more to act on.

"I would have ripped her passport up. There's no way I would have let her leave if I knew now that she was going to the craziest war zone in the world."

The intelligence agency can currently only collect and analyze information and doesn’t have the "mandate to intervene to prevent terror plots from developing," CSIS said in a statement.

While CSIS currently can’t intervene in such a way, it can work with law enforcement partners like the RCMP to detain people believed to be involved in terrorist activities.

Canada has in some major cities integrated national security enforcement teams made up of agencies like the RCMP, local and municipal police, the Canada Border Services Agency and CSIS, which are meant to increase co-operation and information-sharing on national security threats.

The federal government has proposed legislation that would bolster CSIS’s powers. Bill C-51 includes measures that would allow the security agency to disrupt travel plans or financial transactions of people the agency believes have been radicalized.

The Conservative-backed bill faces opposition from the NDP and others who argue it's too broad and doesn't offer sufficient oversight, but it recently passed second reading in the House of Commons and is now headed to committee.

Rabia says her family is furious the alleged recruiter in Edmonton is still free to influence other young Canadians.

She says the online course she believes Aisha was influenced by had 15 Canadian students, and that Aisha was with a Quebec woman during a recent Skype call.

The sisters are still in touch, talking or texting every two weeks, but Rabia says Aisha's tone has changed.

"Over time, reality's kind of showing her another light, and she's realizing it's not what she thought it was. And now her spirit is down. When we speak she sounds really sad and stressed."

Passport revoked

Jeff Weyers, a security researcher who tracks extremists, said the recruitment of Canadian women is concerning.

"You wonder what the attraction is for a female to go to the Islamic State, and join these groups given all the knowledge that we have of what happens to a female in terms of being used in servitude-type roles."

Rabia says she thinks Canada is too focused on "men jihadist fighters, that they're not thinking about the girls. They're just slipping through the cracks.”

She says she’s worried her sister can never come home for fear of imprisonment. Aisha's Canadian passport has been revoked.

“She didn’t do anything for ISIS, she is just there…. cooking for people, helping people in hospitals. She's not out there with a gun in the front lines, because women aren't allowed to do that in Islam and ISIS.”

For now, the family worries about what might happen abroad, but Rabia says the family also understands that there’s likely no way out for Aisha after her decision to leave Canada for the fight in Syria.