But Karen Lewis - who recently referred to the high-stakes talks as "the silly part" of her day - also is a whip-smart Ivy League graduate with a long, distinguished record in the classroom and the overwhelming support of her union's 30,000 members.
Two years after she took the helm of the Chicago Teachers Union, the former chemistry teacher finds herself at the center of a nationally watched confrontation with Emanuel, the equally tough and sharp-tongued former White House chief of staff.
Teachers in the nation's third-largest school district walked off the job Monday for the first time in 25 years after negotiators failed to reach an agreement on issues that include performance evaluations based partly on student's standardized test scores and whether laid-off teachers would have first dibs on job openings districtwide.
The 59-year-old Lewis recently called the mayor a bully and a liar, and their already strained relationship hasn't improved since the strike began.
She seems to be winning the public-relations battle in much of Chicago - for now. Many moms and dads have walked the picket lines with their children, and she's inspired loyalty among teachers in a union long known for infighting. Almost 90 percent of union members voted to authorize a strike.
It all comes down to her credentials and take-no-prisoners personality, supporters say.
During a Labor Day rally a week before teachers went on strike, Lewis called the negotiations "a fight for the very soul of public education."
"The commitment to the children of the city of Chicago is in our hearts, in our minds," she said to a cheering crowd. "It's in the work we do."
Lewis attended public school in Chicago, in the same area where President Barack Obama has a house. The daughter of two Chicago public school teachers, she graduated from Dartmouth as the only black woman in her class. Lewis then taught in Chicago schools for 22 years and became a National Board certified teacher, one of the profession's highest qualifications.
In the classroom, she didn't stand for excuses or bad behavior but was happy to help students who were struggling, said Shannon Carroll, whose daughter had Lewis' chemistry class as a sophomore at King College Prep High School.
Carroll's daughter was having difficulty with the course, so Lewis tested her to see how she learned best. In the evening, she sometimes went over homework with her on the phone.
"She was very patient," Carroll said. "She was the most accessible teacher ever at that school."
Lewis was active in the union for more than 20 years before running for president in 2010. By then, she was a proven leader and well-respected by colleagues, said Ronni Rieck, a teacher who met Lewis while serving on a union executive board together.
"I thought, 'Who is this woman?'" Rieck said.
Lewis came up with creative solutions, Rieck said, and though she was not part of the top leadership team at the time, "they listened to her."
Rieck, who retired in June, said Lewis was more aggressive than some in her determination to push back against the school board when the district began closing dozens of schools and laying off hundreds of teachers while expanding charter schools.
That move, Lewis has said, often forced children to travel long distances or through gang territory, and the union filed a lawsuit to halt the dismissal of teachers.
"She tended to be more aggressive but also tempered that. She wasn't a crazy," Rieck said. "She's a very mature woman and confident in her own skin."
Lewis has sometimes come off as careless and inappropriate, including during a speech to educators and union members last fall in Seattle, where she mocked the way former schools CEO Arne Duncan talked and joked about smoking marijuana at Dartmouth. Lewis apologized to Duncan, who is now President Obama's education secretary. Supporters say she learned from that experience.
"She was trying to be something she wasn't, a comedian, and that's what got her in trouble," Rieck said.
One person Lewis hasn't made amends with is Emanuel, who suggested soon after he was elected that students were getting "the shaft" from teachers because of flat test scores and a graduation rate of just over 50 percent. He rescinded a 4 percent raise, then asked the union to reopen that same contract and accept a 2 percent raise in exchange for working longer hours.
When union leaders refused, he tried to go around them by asking teachers at individual schools to waive the contract and add 90 minutes to the day - until the Illinois Educational Labor Relations Board told him to stop.
During a heated meeting with Emanuel, Lewis has said, the mayor "exploded," used profanity and pointed his finger at her. She also issued a sarcasm-laced statement after learning he would send his children to a prestigious private school.
"We understand why he would choose a school with small class sizes, a broad rich curriculum ... a focus on critical thinking and not test-taking, a teacher and an assistant in every elementary classroom, and paid high-quality professional development for their teachers," she said.
Emanuel, for his part, doesn't take any of the barbs personally and believes Chicago has some of the best teachers in the country, said spokeswoman Sarah Hamilton. But he also has staged photo-ops with idle students to condemn the walkout as a "strike of choice" that disrupted the school year just as it began.
"For him, the only thing personal is about the children," Hamilton said. "It's not about Rahm Emanuel or Karen Lewis. It's about making sure the kids of Chicago get the best education possible."
Rodney Espiritu, a stay-at-home father, said Lewis sometimes seems "hostile and unbending."
"There's a lot of rhetoric from Karen Lewis," he said. "I can understand some of the concerns they have in the classroom, but it seems like ... it's more about the pay."
Juan Jose Gonzalez, Chicago director for the education-reform group Stand for Children, said Lewis "keeps moving the goal post" for reaching a contract settlement. He said union leaders had agreed on many issues, including evaluations, in the spring.
"Now they're saying, 'That's the reason we're striking,'" Gonzalez said. He said Lewis' rhetoric is getting old and predicted parents who respect and value teachers "will become more frustrated with them."
But Rieck said Lewis is being "very rational and very calculated" by ensuring the union exhausts every option before moving to the next step.
"She's navigating real difficult waters," Rieck said. "Now that she's in that leadership role, she really shows a lot of leadership qualities. She understands she has everyone's future in her hands."