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She's thought to have helped convince a teenage girl from London to leave the UK and travel to Syria with two other young girls to join the Islamic State (also known as ISIS), according to BBC.
Mahmood's family is shocked at her involvement with terrorists, and said they had no idea that she had become radicalized, according to the Times.
Her family characterized her as a bright, popular girl who typical teenage girl stuff, including Harry Potter and Coldplay.
The family's lawyer, Aamer Anwar, described Mahmood as "very intelligent, very liked, very bubbly, kind, [and] caring," according to the Times.
But she did, at some point, start wearing a hijab and vocalizing her anger about what was happening in Syria, the Times notes. Still, her family didn't see it as anything that was extremely out of the ordinary.
She was 19 years old in November 2013 when she left her home in Glasgow to travel to Turkey and then on to Syria. Mahmood now goes by the name Umm Layth, or "Mother of the Lion."
Mahmood once wanted to be a doctor or a pharmacist. She is now married to a radical and acts as the "den mother" of those who seek to leave their home countries to join ISIS, according to the Times. The Daily Beast has referred to her as the "Bride of ISIS."
Her family has publicly expressed their horror at what Mahmood has done, calling her a "disgrace," according to the Times. They pleaded with her to get away from ISIS and said her actions are "a perverted and evil distortion of Islam."
Anwar, the family's lawyer, has speculated that she might have become radicalized online. Authorities told CNN that she watched sermons online and communicated with people who convinced her to join the extremists in Syria.
ISIS is trying to build an Islamic state ostensibly governed by a 7th-century interpretation of sharia law in Iraq and Syria.
The group has been recruiting Western women to marry jihadists, as The Daily Beast reported in August.
From The Daily Beast:
Potential caliph-ettes (as one is tempted to call them) are told their main contribution to the Islamic revolution will be through matrimony, not martyrdom; child-bearing, not gun-toting. One blogger called 'Bird of Jannah' purrs: 'Women are not equal to men. It can never be. Men are the leaders & women are [so] special that Allah has given them entire chapter in the Qur'an.'
Mahmood apparently has her own Tumblr blog, cited by the Times and The Daily Beast, that she writes under her pseudonym.
As The Daily Beast notes, "There are no mentions of the public stoning that IS advocates for adultery, nor of the punishments for transgressing strict dress codes, but the constrained lifestyle and the material hardships Western women will face aren't entirely glossed over."
Mahmood made mention of her family in one of her blog posts. She wrote:
Even if you know how right this path and decision is and how your love for Allah comes before anything and everything, this is still an ache which only one [who] has been through and experienced it can understand. The first phone call you make once you cross the borders is one of the most difficult things you will ever have to do…when you hear them sob and beg like crazy on the phone for you to come back it's so hard
In her social media posts, Mahmood has also called for attacks on Western nations.
An estimated 550 Western women have so far traveled to the Middle East to join Islamist groups, according to figures cited by the Times.