Melinda Gates has told Sky News that Donald Trump is not showing the "forward leadership" of France's President Macron.
The philanthropist and wife of Microsoft co-founder Bill Gates also said she was relieved that Congress decides how to spend America's foreign aid budget, and not the president.
Asked what she made of Mr Trump being laughed at at the United Nations, Mrs Gates paused for eight seconds, before answering diplomatically.
"I think we need to have really good leadership in the world," she said.
"And I'm encouraged when I see people like President Macron showing forward leadership.
"To me, that is what the best of democracy stands for.
"And so those are the types of words I'd like to hear from our US president that we're not hearing today."
Kay Burley also asked her what she thought of Mr Trump's assertion that countries would not be getting foreign aid unless they showed America more respect.
Mrs Gates replied: "Luckily, the president proposes a budget and Congress disposes the money.
"I think we have a pretty enlightened Congress – about our foreign aid dollars.
"And we have not, in a very long time as a country, tied those foreign aid dollars to specific statements like that."
Mr Gates added: "I believe that you have to spend foreign aid dollars wisely, and you have to spend them where the greatest disease and disability exists.
"One of the things I think this administration does care about is that the money is actually spent well."
On more personal matters, Mrs Gates said the inheritance her children could expect to get was a private family matter, and "should be kept that way".
However, she said the "vast majority of the resources that have come from Microsoft will go back to society".
Money is clearly a tricky subject for the Gates family, with Mrs Gates revealing that her three children's allowances were kept confidential.
Her kids were "never allowed to tell anyone else what their allowance was and neither was I".
She added: "Because everybody would think it's either too much money – 'Oh my gosh the Gates kids get that much money… or, that's all the Gates kids get?'
"So I think money discussions should remain private inside a family."
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Mrs Gates is in New York for the United Nations General Assembly.
She and her husband, who help developing countries through the Bill and Melinda Gates Foundation, are promoting an initiative called Goalkeepers, setting targets to reduce major problems such as maternal and childhood mortality.