Horne started out with a calm complaint.
"We are going to be doing this all summer long," she said after stepping up to the microphone, referring to a stream of amendments that the flag's supporters were adding to the bill and effectively delaying a vote.
"I cannot believe that we do not have the heart in this body," she said, pausing to swallow her sobs, then raising her voice to shout, "to do something meaningful, such as take a symbol of hate off these grounds on Friday."
She thrust her finger at the floor with every word of her demand.
"And if any of you vote to amend, you are ensuring that this flag will fly beyond Friday. And for the widow of Sen. (Clementa) Pinckney and his two young daughters, that would be adding insult to injury, and I will not be a part of it."
'Enough about heritage'
She was referring to the tragedy that had brought lawmakers to this debate: the June 17 killings, allegedly by a white shooter, of nine black members
of a Bible study at a Charleston church, including the pastor, state Sen. Clementa Pinckney.
Horne, who attended Pinckney's funeral, wanted the flag down badly, believing it to be a symbol of hate and racism.
But before her speech, she listened as a handful of the flag's supporters introduced one amendment after another.
They introduced nit-picking stipulations: Add a new flagpole; dig up flower beds; get budget approval from a museum first; wait a year, then hold a referendum; just go home and think it over some more.
They threatened to create new committee meetings and new legislative sessions to deal with them. If that happened, the flag would keep flapping -- for weeks, months, maybe longer.
By the time Horne got up to speak, fresh grief was simmering under her skin.
She told her colleagues that the suspected shooter, allegedly motivated by racism, had revered the flag for all the wrong reasons and that she was sick of arguments that have kept it aloft for decades.
"I'm sorry, I have heard enough about heritage," she said.
The heritage of the Confederacy is personal for Horne, 42. She says she is a descendant of Jefferson Davis, the Confederate president. But the flag, she said, had to go.
"Remove this flag and do it today. Because this issue is not getting any better with age."
She walked away from the podium and into bear hugs from her African-American colleagues.
In the State House, the proposed amendments kept on coming, but lawmakers kept voting them down.
Finally, early Thursday, the House voted 94-20 to pass the bill to remove the flag.
Horne tweeted out her joy. "It wasn't easy. It wasn't without emotion. But I'm so proud of my colleagues for doing the right thing. The Confederate flag is coming down."
'It took a tragedy to bring this body to this decision'
Gov. Nikki Haley signed the bill Thursday afternoon. At 10 a.m. Friday, the flag will be taken down from a flagpole next to a soldiers' monument, where it has been since early last decade
, when legislators compromised to move it from the pole atop the State House dome.
The flag will be taken to the state's Confederate Relic Room and Military Museum for display.
Horne said Thursday morning she felt "like we have a new day."
"It's bittersweet, because it took a tragedy to bring this body to this decision," Horne told CNN's "New Day." Referring to the Charleston shootings, she said she felt the General Assembly met "tragedy with triumph and defeat with purpose."
"I am so proud to be a South Carolinian and proud of what South Carolina has done to move this state forward."
Her speech had been heard across the country and found resonance in social media in South Carolina and as far away as California.
"If you're looking for who to thank for getting #ConfederateFlag down: @JennyHorne, @GCobbHunter who kept up the fight. Thank you SC," Shawn Drury, who says he's from South Carolina, posted to Twitter.
"Your speech was beautiful. Thank you for being such a warrior for peace," posted Kelly Carlin from California.