Jane Merrick is a British political journalist and former political editor of the Independent on Sunday newspaper. The opinions expressed in this commentary are hers.

(CNN) When Theresa May stood outside Downing Street one year ago Thursday after being officially appointed Prime Minister of the United Kingdom of Great Britain and Northern Ireland by the Queen, her vision for Britain was ambitious.

Her visit to Buckingham Palace had given her a statesmanlike air as she pledged to tackle society's injustices, reassuring all voters she understood their concerns about job security and her offering to help those who were "just about managing."

Never before or since has she looked more powerful.

Now it is her own job security that is the pressing issue inside Downing Street. It is she who is just about managing -- to keep control of her party, Brexit and her government majority.

Anniversaries are supposed to be opportunities for celebration. Yet May could be forgiven for reflecting ruefully on the disastrous year she has had.

Her problems started well before her calamitous decision to call a snap election in April. Sure, she enjoyed a honeymoon in her first few months as Prime Minister -- in the sense that her own personal and party poll ratings soared , and she faced few critical newspaper headlines. But her real underlying difficulties were being masked by this apparent popularity.

It is arguable that her honeymoon -- and the perceived weakness of her left-wing, Labour opponent Jeremy Corbyn -- lulled May into a false sense of her own security. This, ultimately, laid the foundation for a hubristic election campaign that ended in near disaster and the Prime Minister losing her parliamentary majority.

May failed to define Brexit from the moment she became Prime Minister, coming up with the meaningless phrase "Brexit means Brexit," which became a point of humor and then ridicule.

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She alienated business with her speech to the annual Conservative conference in October by warning companies not to treat workers badly or ramp up excessive pay. In January she finally gave a definitive speech on what Brexit under her government would mean, but that same month she was defeated by the Supreme Court over her refusal to let members of Parliament have a vote on triggering Article 50, the mechanism that started the two-year Brexit process.

She failed to use her first few months to define herself as anything other than a change from her predecessor, David Cameron. This lack of definition meant there was no substance behind her election campaign slogan, "strong and stable leadership."

Yet if May thinks her first year in office has been bad, year two is about to get a whole lot worse. After losing her majority and having to cobble one together with Northern Ireland's Democratic Unionist Party, her government is unable to pass any controversial laws.

She has already had to concede on two issues: allowing women from Northern Ireland to travel to mainland Britain for abortions and announcing a public inquiry into a contaminated blood scandal.

Thursday also marks the publication of the Great Repeal Bill, which undoes Britain's legal ties to the European Union and transfers all EU law from Brussels to Westminster, placing these laws on the UK statue book. The point of this to create the smoothest transition possible in the days after Brexit happens.

Its grand name, conceived during May's period of strength, is now freighted with irony, as it will struggle to get through Parliament without being heavily amended by opposition parties.

Her government is now doomed to spend most of its time over the next 12 months trying to negotiate its way to Brexit -- both in the House of Commons and with the EU. There will be little time to achieve anything else. The country will be practically ungovernable.

Those Brexit negotiations with the EU are themselves already in difficulty: There is disagreement across the board, including on the rights of EU citizens living in the UK, which was supposed to be an early concession from May.

The Prime Minister is weak in the eyes of the public, who took a dim view of her handling of the Grenfell Tower block disaster, and she is weak in the eyes of her own Conservatives, who are actively looking for a successor.

While there will be no immediate challenge to her leadership as members of Parliament prepare to start their summer break next week, the Tory party conference in the autumn will renew focus on her weakened authority.

Given this outlook, May must be wishing she could rewind the clock to a year ago, when all power and control over her party and the country were at her feet. It is by no means clear whether she will have the opportunity to celebrate a second anniversary.