Millions of people across the UK and beyond have come to recognise her tenacity.
In the end however, the prime minister had lost too much political support within her own party.
When Mrs May got emotional in Downing Street yesterday as she announced her departure, few people will have doubted her patriotism. Her commitment to Northern Ireland and unionism was also clear. All four Tory prime ministers of the last 40 years have been unionist: Margaret Thatcher, John Major, David Cameron and Mrs May.
But like Mrs Thatcher and the 1985 Anglo Irish Agreement, Mrs May was persuaded that to secure her unionist vision she had to agree to significant constitutional change for the sake of political harmony and wellbeing on the island of Ireland. The end result was the backstop of 2017.
Had that backstop merely resulted in constitutional damage to Northern Ireland, Mrs May might have survived. But in her determination to avoid a border of any type, in the Irish Sea or at land, Mrs May had to dilute UK-wide Brexit, and so alienated grassroots Brexiteers.
She made a massive error in accepting the EU insistence that the Irish border matter be settled before the UK could even get agreement on the terms of its departure from the EU. The question now is whether her successor will have the will to rectify that blunder.