When she stopped by a Middle Eastern bakery for lunch, she refused to purchase a water bottle, in spite of the summer heat, because it was manufactured by Nestle, which has increased the volume of water it pumps from Lake Michigan.

“My community wants me to work on economic justice,” she said. “I am not for the privatization of water.”

When it comes to policy, Ms. Tlaib said she is mostly concerned with local issues, like Michigan’s high car insurance costs and creating “neighborhood services centers” — reimagined district offices that offer community resources like free tax preparation or energy grants. She plans to spend as much time as possible in Michigan, not Washington, and even wondered whether it was possible to move her swearing-in ceremony to Detroit. “If people want to meet with me, they can come here,” she said.

Asked how she proposes to pay for Medicare For All, she pulled up the Department of Defense website and read aloud from its daily announcements of new contracts, some earmarked for hundreds of millions of dollars. “This is unbelievable,” she said. “Oh and by the way, this was just for the Navy.”

She sees standing up for Muslims and Arab-Americans amid the rise of Islamophobia as part of her broader civil rights ambitions for all Americans. The morning after Mr. Trump won the presidency, Ms. Tlaib called her mother, Fatima Elabed, who was out shopping for groceries while wearing her hijab, to ask if she was O.K. A man was yelling at her to take it off, Ms. Tlaib remembered, and her mother replied, “You don’t understand, Jesus was born in my country.”

On Friday afternoon, as Ms. Tlaib boiled water for tea in her small Detroit apartment, it was her mother who called, worried, she said, “that America will start hating my daughter,” after she saw angry comments about Ms. Tlaib on social media.

It is the logic of the political system itself, not just of the electorate, that Ms. Tlaib wants to change. “When I say, ‘We need to come from a place of love,’ people roll their eyes and snicker,” she said of elected officials.