In a Twitter aside during his election campaign, Donald Trump dismissed the UN as “just a club for people to get together, talk and have a good time”. For Amina Mohammed, the organisation’s new deputy secretary general, it is anything but.

Attempting to meet some of the world’s most intractable crises and developmental challenges head on is what drives the focused Mohammed, for whom battling against the odds has been a lifelong theme.

The former Nigerian environment minister once confided that she had to raise money when she wanted to study hotel catering management in Italy.

“I said to my father: ‘I’m leaving,’” Mohammed told me. “He said, ‘OK, but I have no money to give you’. So I challenged everyone and said I am walking from Kaduna to Zaria – which is 76km – to raise the cash. They all said ‘You can’t do it!’ But I raised £4,000, and that was it, I was off.”

In a rare moment of self-reflection as we sit in her office on the 38th floor of UN headquarters in New York recently, she said:“For me, it has been a long journey, step by step, using the education I had to make a difference.”

The journey has indeed been long, all the way from a primary school by Lake Chad to a place at the side of UN chief António Guterres, torchbearer of a sprawling organisation that, for all its very publicly displayed weaknesses, is of such vital importance to the global south.

Even Mohammed’s CV is a marathon. She is the eldest of five daughters and now a mother of six children. Her father, a Nigerian herdsman and a vet, met her mother, a nurse, while studying in Britain. After Mohammed finished her studies in Italy, her father demanded she return to Nigeria, and to a job – he promised – at the American consulate in Kaduna. When she arrived, though, it quickly became apparent there was no job.

“So I walked around and around and, eventually, I was 11 years at an architectural design office in northern Nigeria. It was tough being a single woman and going into offices,” she says. “The men would say, ‘Why is she here?’ They also often thought I couldn’t speak the native languages, so I would hear an awful lot of stuff they thought I couldn’t understand, I can tell you.”

After years in the private sector, Mohammed served three Nigerian presidents before becoming adviser to Ban Ki-moon, Guterres’ predecessor as secretary general, on the post-2015 development agenda.

Amina Mohammed speaks at a UN event on using technology to support implementation of the sustainable development goals. Photograph: Evan Schneider/UN Photo

Now back at UN headquarters after a brief stint as environment minister in Nigeria, her development and environment brief is as sharp and specific as the 17 sustainable development goals she helped to hone down from the 500 or so originally proposed by member states.

With global cooperation and solidarity key to achieving the goals by 2030, the Trump administration’s very public disdain for climate issues has obvious implications for the Paris climate change agreement. Mohammed stresses the importance of shared responsibility, of trying to pick up any countries that might stumble en route to seeing the process through.

“Remember when everyone was smoking everywhere, whether it was in a plane or a train or in restaurants, and we thought we shouldn’t do that any more and stopped smoking in public places? The minute that science proved smoking would have an effect on the pregnant woman next to you, your conscience, the moral imperative, was for you to drop the cigarette and walk outside. So I think there is a collective responsibility for major emitters, and that underpinned everything we did in Paris.”

Mohammed knows whereof she speaks. After Paris, she visited Lake Chad to witness the effects of climate change at first-hand. Her childhood stamping ground had changed beyond recognition.

“Here I was, maybe 40 years later, looking at it, and it was a tenth of the size it was. It is in an area where, of course, terrorism has taken hold and all the livelihoods are lost; the fishing lost, no jobs, no trade. In our youth there used to be trailer loads of fish going from the north down to the south – that’s lost. This has exacerbated poverty, it has created a sense of no hope, a lack of governance.”

Mohammed is determined there will be no comparable lack of governance at the UN. As the organisation braces itself for a whirlwind of proposed cuts under the Trump administration, the new leadership in Turtle Bay is committed to ensuring the UN remains capable of delivering on its development, peacekeeping and many other commitments.

Still, how do you go about persuading Trump, like Ronald Reagan before him, that the UN is good value for money? Mohammed is characteristically unfazed. “We don’t always communicate very well the effect that we have on the ground and the lives that we change. That needs to be done better and, once we have the changes, we will see the United States doing probably even more.”