"He's the problem-solver," Cooper said of Rendell. "My job is to come up with options. He's the one that solves the problems."
Although her suggestion helped get the deal done - the budget was signed by Rendell Friday after a 101-day impasse - Cooper doesn't claim credit for breaking the logjam.
You won't see her at press conferences, political rallies or TV talk shows. But talk with people who know the state Capitol and they'll tell you: She's probably the most powerful woman in Pennsylvania.
As director of Rendell's policy office, Cooper is the governor's closest adviser on a wide range of issues.
It was Rendell's commitment to a core policy goal of Cooper's - boosting education funding even in a fiscal crisis - that made a budget deal so hard to achieve from the beginning.
"I think Donna Cooper is the heart and soul of the Rendell administration," said attorney John Estey, who served as Rendell's chief of staff in his first term.
"If you look at all of the areas where the governor has made a stand over the years on social issues, she's behind every single one of them," said former Rendell senior adviser Ken Snyder.
Rendell describes Cooper as someone who "brings an incredible passion that keeps us all on our toes.
"We're in a business where most people have become passionless implementers, looking for the least dangerous path," Rendell said last week.
"To have someone like Donna around you who says, 'Let's let 'er rip, some things are worth fighting for,' to me as a decision maker, that's inspiring."
Cooper has a background in social activism and was a leading state education advocate, but her influence in the administration stems from her intimate grasp of policy issues and a relationship with Rendell that dates back to his days as mayor of Philadelphia.
While Cooper's intelligence and work ethic are widely respected, some in the Capitol see her as an abrasive know-it-all, referring to her derisively as "Governor Cooper."
"Sure, she grates on legislative leaders and on Cabinet secretaries," said Pete DeCoursey, a veteran Harrisburg reporter and bureau chief for the online news service Capitolwire.
"But people who've had that job for other governors have had the same problem." DeCoursey said. "Policy secretaries are always the most hated people in the administration, because their job is to advance the governor's agenda. Others seek compromise.
"I think Donna may generate a little more negativity than others because she's a tough-minded woman in a culture where that's the exception rather than the rule," DeCoursey said. "And some people don't like what they see as the aggressive Philadelphia personality."
"I'm not mean, but I'm direct," Cooper said in an interview. "This is not a love fest. I always say that if you want someone to give you b-s, go to another office. I'll tell you what I think."
As policy secretary, Cooper has a team of seven in her office, and works with policy staff in virtually every department and agency in the executive branch of the government.
She describes a typical day as "like 'West Wing' on speed."
"There are lots of decisions that have to be made quickly, often about complex issues," Cooper said. "Some are big things that have to be taken care of immediately. Some are little things that can't be ignored and allowed to grow into big things.
"It's everything from what to do about a federal court interfering with state control of air regulations, to a story in a rural paper that criticizes us for not having lifeguards in state parks," she said.
She also has nearly constant access to the governor. It's a relationship that has grown over time.
Cooper first went to work for Rendell in 1992 as head of the Mayor's Commission on Literacy. Her resumé included organizing to stop a nuclear plant in Bali, three years at the Washington Peace Center, working as an aide to the mayor of Reading and staffing Joe Vignola's U.S. Senate campaign.
Over the next five years, Rendell came to rely increasingly on Cooper to take on policy challenges, such as working on the successful application for federal Empowerment Zone assistance, and organizing the city's response to welfare reform. Rendell eventually made her deputy mayor for policy and planning.
After Rendell left City Hall, Cooper became executive director of Good Schools Pennsylvania, an education advocacy group. There she built a statewide campaign for education funding reform and stayed in touch with Rendell.
School funding reform became a key plank of Rendell's 2002 gubernatorial campaign, and when he made Cooper his policy chief, it remained an enduring priority of the administration.
Estey said that Cooper's influence is clear, but said that Rendell held firm on school funding because he believes in it. Cooper is happy he does.
"It's why I'm here," Cooper said. "That's why I work for Ed Rendell, because it's his agenda."
But Cooper isn't just an education specialist. Her policy reach has expanded throughout the government since she joined the administration in 2003. Several aides said that now she's remarkably fluent in nearly everything state government touches.
Last year, Rendell gave her the responsibility for developing the state's strategy for influencing President Obama's stimulus legislation, which involved immersion in a dizzying matrix of state needs, federal regulations and congressional proposals.
Michael DiBerardinis, a longtime friend of Cooper's who headed the State Department of Conservation and Natural Resources, said that Cooper's knowledge of state and federal policy "just exploded" when she came to the Capitol.
"With all that energy and intellect she could wrap around the job, she became a real standout," DiBerardinis said. He said that it's also remarkable to see the relationship she's developed with Rendell over seven years in Harrisburg.
"They've had such a close day-to-day relationship," DiBerardinis said, "that they now communicate so honestly and directly that they get a lot done in a short period of time. Every word [between them] is understood, and they share so much knowledge of every issue. It's impressive to be in a room and see that."
While Cooper may have mastered policy in Harrisburg, she hasn't made it her home.
She and her husband, Arthur Meckler, an Old City antique dealer, still own their rowhouse in Fishtown. Cooper typically spends Monday through Thursday in Harrisburg and works Friday and many weekends at the governor's office in the Bellevue, in Center City.
Cooper, who works long days and gets to the gym to stay in shape, said that she looks forward to returning to her Philadelphia neighborhood when her time in Harrisburg ends.
But she has no plans to abandon her policy passions.
"When I come home I envision working on education issues, or on welfare-to-work, both at the policy and direct-service levels," Cooper said. "I loved working with women on public assistance, helping them navigate a way to independence."
Her options could change if Rendell becomes a Cabinet secretary or takes another job in Washington after he leaves office at the end of next year. If the past is any guide, he's likely to want Cooper on his team.