Introducing others to Jimi Hendrix, street art, and talking politics was not supposed to get her killed. But in Pakistan, free speech is dangerous, and Mahmud's exuberant exercise of it made her stick out nationwide.
Two gunman shot her dead at point-blank range late Friday after she locked up The Second Floor cafe in Karachi for the night, police said. Mahmud died from five bullet wounds.
The gunmen also shot her mother. She is in a hospital but is expected to be released on time for her daughter's funeral.
Mahmud's killing broke hearts beating for non-violence and progressive values across the country. She freely said what she thought in a place where many people are too afraid to and by doing so spoke for many more people than just herself.
She had become a Pakistani figurehead for humanism, love and tolerance.
"She took that torch into the dark forest and so many people followed. She really, truly was a success story of the heart," said close friend and BBC journalist Ziad Zafar.
Uncomfortable topic: disappearances
No one has claimed responsibility for her shooting, and police have not named any motive. But Mahmud had just finished leading a discussion group on a topic that many want silenced, when the shots fell.
In the province of Baluchistan, where separatists have fought a virulent insurgency for years, people have been disappearing regularly. There have been steady allegations of mass abduction. The Lahore University of Management Sciences planned to host the discussion on the topic, with human rights activist Mama Qadeer Baloch, but authorities shut it down.
Mahmud would not hear of it not going on.
"Despite the plurality of opinion, very little space seems to be given to the discussion in Pakistani mainstream media or academia; the debate seems to be shut down before it can even begin," she posted on Facebook. "What is the reality? Has the media been silenced on Balochistan? What makes it dangerous for us to talk about Pakistan's largest province at one of our most celebrated universities?"
She invited the discussion to The Second Floor, also known by the shorthand T2F. She said she knew it was a potentially dangerous move, and she had received death threats in the past when she handled the topic before.
"She was the bravest woman in the world, she really was, she was a brave heart; my God, she was a brave, brave girl," Zafar said.
A magnet of enlightenment
Even in its secluded, humble location, T2F was a magnet to those seeking secular wisdom. They found it in a homey setting, musingly decorated like a small town college bookstore. The walls outside its entrance are sprayed with socially critical graffiti -- dusky red hearts float across gray walls.
Mahmud waited to greet visitors, many of them young Pakistanis seeking freedom of thought, with a hug, a mug and encouragement for Pakistan's future. "She hoped the same thing we all hoped for, a place that is fair with liberty and justice for all," Zafar said.
Grief over her death and gratefulness for her work poured out on social media and via email.
"Thanks for giving us the room to breathe when fog pressed heavy on our shoulders. It's only been a few hours, Sabeen, and the city is already gasping for air," a group of illustrators called From Karachi with Love wrote.
An artist drew Mahmud puttering off on a Vespa scooter wearing pants, a blouse and sandals. Her tightly coiffed short hair and angular glasses framed her bright-eyed features. Missing was a head scarf.
On a wall in T2F is a spray painted Technicolor image of Marilyn Monroe from "the Seven Year Itch," her white dress replaced by a traditional outfit of mustard, ocher and green.
But it still flew up over her hips, revealing her alabaster legs, a daringly sexy and satirical image. The artistic expression sticks out and triggers passions, like many things Mahmud said and did.