LONDON — Last week, for the first time in six months, Prime Minister Theresa May enjoyed a few hours of sweet vindication in her efforts to allow the United Kingdom to leave the European Union. She had passed the night in white-knuckled negotiation, and by sunrise was able to announce the beginning of talks that would lay out a path to a controlled departure.

Another politician would have crowed a little, or luxuriated in the moment. But not Mrs. May. She landed from negotiations in Brussels and her motorcade rushed straight from the airport to a neighborhood of neat, red-brick houses, where she attended a gathering of Alzheimer’s patients, followed by a fund-raiser for a children’s hospice and a Christmas tree festival. No reporters were invited. She showed up because she had promised to be there.

The same old-fashioned, unglamorous, dutiful approach has guided Mrs. May, 61, throughout her struggle to guide the country’s withdrawal from the E.U., known as Brexit. There are no victory laps. Instead she plows forward, scrambling to her feet after each roundhouse blow, most recently on Wednesday night, when Parliament secured the right to approve — or veto — her final deal.

She has been undermined by her own cabinet ministers, derided as pitiful in Brussels and mocked in the news media as a “dead woman walking.” Though the only other woman to hold the post of prime minister, Margaret Thatcher, was able to transcend her gender, Mrs. May has been hemmed in on all sides by stereotypes — first criticized as a humorless headmistress, not human enough to be likable, and then as too human, and therefore weak.