It is hard to find anyone more passionate about the idea of steering public dollars away from traditional public schools than Betsy DeVos, Donald J. Trump’s pick as the cabinet secretary overseeing the nation’s education system.

For nearly 30 years, as a philanthropist, activist and Republican fund-raiser, she has pushed to give families taxpayer money in the form of vouchers to attend private and parochial schools, pressed to expand publicly funded but privately run charter schools, and tried to strip teacher unions of their influence.

A daughter of privilege, she also married into it; her husband, Dick, who ran unsuccessfully for governor of Michigan a decade ago, is heir to the Amway fortune. Like many education philanthropists, she argues that children’s ZIP codes should not confine them to failing schools.

But Ms. DeVos’s efforts to expand educational opportunity in her home state of Michigan and across the country have focused little on existing public schools, and almost entirely on establishing newer, more entrepreneurial models to compete with traditional schools for students and money. Her donations and advocacy go almost entirely toward groups seeking to move students and money away from what Mr. Trump calls “failing government schools.”

Conservative school choice activists hailed her on Wednesday as a fellow disrupter, and as someone who would block what they see as federal intrusion on local schools.

Former Gov. Jeb Bush of Florida, where Ms. DeVos helped push legislation establishing tax credits for scholarships to private schools, called her an “outstanding pick,” a “passionate change agent to press for a new education vision.”

“Her allegiance is to families, particularly those struggling at the bottom of the economic ladder, not to an outdated public education model that has failed them from one generation to the next,” he wrote on Facebook.

Frederick M. Hess, the director of education policy studies for the conservative American Enterprise Institute in Washington, called Ms. DeVos a “smart, principled small-government conservative who’s experienced in politics and versed in the relevant policy.”

But to teachers’ unions, she is anathema.

Randi Weingarten, the president of the American Federation of Teachers, called Ms. DeVos “the most ideological, anti-public education nominee” since the secretary of education was elevated to the cabinet level four decades ago.

Even some groups that share her support for charter schools worried that picking someone so closely identified as a champion of vouchers signaled that the Trump administration would try to starve public schools.

As a candidate, Mr. Trump proposed steering $20 billion in existing federal money toward vouchers that families could use to help pay for private or parochial schools, perhaps tapping into $15 billion in so-called Title I money that goes to schools that serve the country’s poorest children. He called school choice “the civil rights issues of our time.”

Amber Arellano, the executive director of the Education Trust-Midwest, an advocacy group in Michigan that supports charters but has been critical of a Michigan charter school law that Ms. DeVos has spent millions to defend, said the pick had “the potential to undermine the nation’s hard-won progress by diverting resources from the young people who most need them, or by failing to uphold the federal government’s responsibility to protecting the needs and interests of all students — especially the most vulnerable.”

Michigan is one of the nation’s biggest school choice laboratories, especially with charter schools. The Detroit, Flint and Grand Rapids school districts have among the nation’s 10 largest shares of students in charters, and the state sends $1 billion in education funding to charters annually. Of those schools, 80 percent are run by for-profit organizations, a far higher share than anywhere else in the nation.

The DeVoses, the most prominent name in state Republican politics, have been the biggest financial and political backers of the effort.

But if Michigan is a center of school choice, it is also among the worst places to argue that choice has made schools better. As the state embraced and then expanded charters over the past two decades, its rank has fallen on national reading and math tests. Most charter schools perform below the state average.

And a federal review in 2015 found “an unreasonably high” percentage of charter schools on the list of the state’s lowest-performing schools. The number of charter schools on that list had doubled since 2010, after the passage of a law a group financed by Ms. DeVos pushed to expand the schools. The group blocked a provision in that law that would have prevented failing schools from expanding or replicating.

Ms. DeVos, 58, got into education advocacy primarily as a backer of vouchers, and has served on the board of several organizations that have campaigned for them across the country.

A ballot initiative she led to establish vouchers in Michigan failed in 2000. The next year, she established the Great Lakes Education Project, which became an ardent proponent of charter school expansion, and has donated generously to candidates who have supported it.

The Michigan law pushed by Ms. DeVos to establish charter schools 20 years ago allows an unusually large number of organizations to start such schools, yet established little mechanism for oversight. Even Republican supporters of charter schools say the law has allowed failing charter schools to expand or replicate.

Last spring, the DeVos-backed group was the chief force behind the defeat of legislation that would have established standards for identifying and closing failing schools, both charter and public, in Detroit, where a flood of charter schools in the past decade has created what even charter school supporters call chaos.

Ms. DeVos was born in Western Michigan, the more conservative and religious part of the state, where her father created a successful auto parts company. Her brother is Erik Prince, the founder of Blackwater, the troubled private security contractor that was awarded billions in United States government contracts in the Middle East.

Like many conservatives who supported Mr. Trump, she does not support Common Core, the set of standards for what students should know at each grade level that was developed by the National Governors Association and other groups — and that has been incorrectly branded as a federal policy.

She also had not supported Mr. Trump; her family was behind Senator Marco Rubio of Florida in the Republican presidential primary.

On Wednesday, she wrote on Twitter: “I am honored to work with the president-elect on his vision to make American education great again. The status quo in ed is not acceptable.”