Shafiqah Hudson was looking for a job in early June of 2014, toggling between Twitter and email, when she noticed an odd hashtag that was surging on the social media platform: #EndFathersDay.

The posters claimed to be Black feminists, but they had dubious handles like @NayNayCan’tStop and @CisHate and @LatrineWatts. They declared they wanted to abolish Father’s Day because, they said, it was a symbol of patriarchy and oppression.

They didn’t seem like real people, Ms. Hudson thought, but parodies of Black women, spouting ridiculous propositions. As she told Forbes magazine in 2018, “Anybody with half the sense God gave a cold bowl of oatmeal could see that these weren’t feminist sentiments.”

But the hashtag kept trending, roiling the Twitter community, and the conservative news media picked it up, citing it as an example of feminism gone off the rails and “a neat illustration of the cultural trajectory of progressivism,” as Dan McLaughlin, a senior writer at National Review, tweeted at the time. Fox News devoted a segment of its “Fox & Friends” show to lampooning it.

So Ms. Hudson set out to combat what she realized was a coordinated action by trolls. She created a hashtag of her own, #YourSlipIsShowing, a Southernism that seemed particularly useful about calling out people who think they are presenting themselves flawlessly.

She began to aggregate the trollers’ posts under the hashtag and encouraged others to do so, and to block the fake accounts. Her Twitter community took up the mission. They included Black feminists and scholars like Ra’il I’Nasah Kiam, who did some digging and discovered that #EndFathersDay was a hoax, Slate wrote in 2019, organized on 4chan, the dark community of web forums peopled by right-wing hate groups.

Twitter, Ms. Hudson and others said, was largely unresponsive. Nonetheless, their actions were effective. #EndFathersDay was pretty much silenced within a few weeks, though fake accounts continued to pop up over the years, and Ms. Hudson kept calling them out, like an endless game of Whac-a-Mole.

Yet #EndFathersDay, it turned out, was more than a joke. It was a well-structured disinformation action. As Bridget Todd, a digital activist who interviewed Ms. Hudson in 2020 for her podcast, “There Are No Girls on the Internet,” put it, it was a kind of test balloon for the election-disruption campaign that began in 2016 with tactics by Russian agents, as Senate hearings showed. In hindsight, Ms. Hudson’s efforts added up to an early and effective bulwark against misinformation that can threaten democracy.

“It should be validating,” Ms. Hudson told Slate. “But instead it’s been upsetting and alarming. Nobody wants to be right about how much real peril we’re all in, even if you saw it coming.”

Ms. Hudson, a freelance writer who had worked in nonprofits but who from 2014 on had dedicated herself to Twitter activism, died on Feb. 15 at an extended-stay hotel in Portland, Ore. She was 46.

Her brother, Salih Hudson, confirmed her death. He said that he did not know the cause, but that she had Crohn’s disease and respiratory. Her followers were told in her posts that she had long Covid and had recently been diagnosed with cancer — and that she had no money to pay for her care. Many pitched in to help.

Her followers expressed frustration and anger that Ms. Hudson had never been paid by the tech companies whose platforms she policed, that she had not been properly credited by scholars and news organizations that cited #YourSlipIsShowing, and that she had not received the health care she needed.

“The world owed Fiqah more than it gave her,” Mikki Kendall, a cultural critic and author of “Hood Feminism: Notes From the Women That a Movement Forgot” (2020), said by phone. Ms. Kendall is one of many Black feminists who took up Ms. Hudson’s mission and befriended her on Twitter, which is now called X.

“The world owes Fiqah to never let this happen to anyone else again,” Ms. Kendall said. “Unfortunately, she exists in a long tradition of Black activist women who die impoverished, who die sick and alone and scared, because we love an activist until they need something.”

Shafiqah Amatullah Hudson was born on Jan. 10, 1978, in Columbia, S.C. Her father, Caldwell Hudson, was a martial arts instructor and author. Her mother, Geraldine (Thompson) Hudson, was a computer engineer. The couple divorced in 1986, and Shafiqah grew up with her mother and brother, mostly in Florida, where she attended the Palm Beach County School of the Arts, a magnet school.

She earned a B.A. in 2000 at Hobart and William Smith Colleges in Geneva, N.Y., majoring in Africana studies with a minor in political science. After graduating, she moved to New York City and worked at various nonprofit organizations.

She was new to the city and lonely. She found community on blogs and social media sites, including Twitter, which she joined in 2009. (She chose as her avatar an image of Edna Mode, the imperious fashion maven from “The Incredibles.”) And like many Black women on that platform, she was mocked and harassed. She received rape and death threats, she told Ms. Todd.

In addition to her brother, Ms. Hudson is survived by her father and her sisters, Kali Newnan, Charity Jones and Mosinah Hudson. Geraldine Hudson died in 2019.

In the last months of her life, Ms. Hudson posted about her deteriorating health and her fears of not being able to pay for her care or housing. She was unable to work because of her disabilities.

She had moved to Portland, her brother said, because the climate was better for her respiratory ailments. But she was not able to secure health insurance. Doctors had discovered that the painful fibroids from which she suffered were cancerous. She needed money for more biopsies and for transportation to the hospital. Her Twitter community chipped in, as always. She did not ask her family for help.

“She was very private and very proud,” Margaret Haynes, a cousin, said by phone, adding that she had spoken to Ms. Hudson a few weeks before her death. “She told me: ‘I’m good. If I need something, you’ll be the first to know.’”

Yet on Feb. 9, Ms. Hudson told her followers: “I feel like I’m meowing into the void. And it’s raining. And I’m just trying not to drown.”

Feb. 7 had been a tough day. Ms. Hudson was dizzy and in pain, she wrote. She was feeling her mortality and posted about her decision to be single and not have children — “to be an Aunt(ie) and not a mom,” as she put it, recalling a conversation she’d had with a young family member.

She died eight days later.

Alain Delaquérière contributed research.