Mrs May has indicated she will be willing to challenge the new US President when "something is unacceptable"
The British Prime Minister has confirmed she will meet President Donald Trump for talks on Friday.
It appears likely the British Prime Minister will be the first foreign leader to meet the new President since his inauguration.
In an interview with BBC, she said: "I have already said that some of the comments Donald Trump has made in relation to women were unacceptable. Some of those he himself has apologised for."
She suggested she will be willing to challenge the new president when warranted, saying "it is the special relationship that allows us to say when something is unacceptable".
Mrs May also argued that her decision to meet with Mr Trump would send a "big statement about the role of women".
A White House senior administration official confirmed previously that Mrs May "will be at the White House this coming week to meet with President Trump", but did not say on which day.
Mr Trump later added that the visit would happen "very shortly".
It has been suggested that Steve Bannon, Mr Trump's chief strategist, expressed a desire for the two leaders to meet sooner rather than later for a "business-like" visit.
In an interview with the Financial Times, Mrs May said she would urge Mr Trump when she meets him to recognise the importance of NATO and not to undermine European unity.
She said she expected to have "very frank" discussions with the new President and wanted to make early progress towards a US-UK trade deal.
"The importance of the co-operation"
Talking in her Maidenhead constituency on Friday, Mrs May said she was sure the President "recognises the importance and significance of NATO".
She added: "I'm also confident the USA will recognise the importance of the co-operation we have in Europe to ensure our collective defence and collective security."
On trade, she said: "I'm confident we can look at areas even in advance of being able to sign a formal trade deal.
"Perhaps we could look at barriers to trade at the moment and remove some of those barriers to open up that new trading relationship."
It has been reported that Mr Trump and his team want to embrace comparisons with Ronald Reagan and Margaret Thatcher, who were political soulmates during the 1980s.
But Mrs told the FT: "As you know, I'm not someone who goes around with a model I want to emulate from the past.
"When he says that he means he wants it to be a very special relationship and I'm confident we can make it such."
The first meeting between the two leaders - often called a "get acquainted trip" in Washington - will not include any glittering social events or a visit to Camp David, the President's country retreat.
The Sunday Times says Mrs May is due to see Mr Trump in Washington on Friday after visiting Philadelphia on Thursday to meet senior Republican leaders from Congress, who will have to approve any US-UK free trade deal.
She will reportedly address a Republican "congressional retreat" and hold talks with Paul Ryan, the speaker of the House of Representatives, and Mitch McConnell, the Senate majority leader.
When she is in Washington, Mrs May is expected to offer Mr Trump a return visit, likely to include a state banquet hosted by the Queen at Windsor Castle or Buckingham Palace.