According to the social media accounts of citizen journalists from Raqqa, Hassan was killed sometime late last year. But ISIS only informed her family of her death this week, saying she had been "executed" for "espionage." CNN is unable to independently confirm the circumstances of her death.
It's believed to be the first time that ISIS has killed a female citizen journalist in Syria.
Hassan was known by the pseudonym Nisan Ibrahim and was one of a number of young activists in Raqqa who tried to get word to the outside world of what was really happening in the city.
Her social media photographs show a self-assured, clear-eyed young woman in a head scarf. She has a calm smile that looks like it's about to break into laughter. She wears bright pink lipstick.
She wrote about everyday life under ISIS rule, about coalition airstrikes as they rocked the city -- with humor, sadness and a glint of hope.
Her last postings were in July. They were a mixture of the wistful and defiant, and full of prayers.
Hassan posted a photograph of an old TV antenna, with the caption "A little to the right. Yes, yes, no, now a little to the left... no it's not working. You come down and I'll go up. Remember... those were the best days."
As coalition planes circled overhead on July 15, she offered a prayer: "God protect the civilians and take the rest."
And she captured life in the city in vivid ways. "People at the souq (market) are like waves crashing into each other... not because of the numbers... but because people's eyes are glued to the sky... their eyes move above in fear while their bodies move unconsciously below."
Hassan mocked ISIS' attempts to ban Wi-Fi hotspots in Raqqa.
"Go ahead and cut off the internet, our messenger pigeons won't complain," the post read.
Then on July 21, her Facebook postings abruptly stopped.
On that day, her last posts reveal a reflective mood, yearning for normalcy in a city where she was hunted as a spy.
"Sometimes we think of something and it happens... or thinking of someone and the next day we run into them by chance or get a call from them," Hassan posted.
"These days I'm thinking about rest... about peace... about safety... about feeling reassured..."
She was never to find that rest and peace. Maybe she didn't expect to. She wrote the same day: "Our biggest mistake was to swim in a sea of dreams... and we dreamt of the next phase and ignored the current phase... we look at the future and forgot the past... #a mistake we regret."
Abu Mohammed, who founded the activist group Raqqa Is Being Slaughtered Silently, tweeted that among Hassan's last communications were these words: "I'm in Raqqa and I received death threats, and when ISIS (arrests) me and kills me it's ok because they will cut my head and I have dignity it's better than I live in humiliation with ISIS."
In recent months, several of the Raqqa group have been assassinated in Turkey
or killed inside the so-called caliphate established by ISIS, of which Raqqa is the administrative headquarters.
Hassan came from a Kurdish family that was originally from the town of Kobane, Syria, on the Turkish border. The family had at some date relocated to Raqqa.
In a country where education was open to women, Hassan grasped her opportunities, studying philosophy at the University of Aleppo, according to the website Syria Direct. She wanted a free and democratic Syria, and joined opposition protests in Raqqa in 2011. Then ISIS arrived, and she had to go underground, as did so many activists for whom the ideals of the Syrian revolution were the opposite of what ISIS' caliphate offered.