Kim Bellingham’s stepson was killed while clearing a mine area and she said: “He’d been called through because someone had been injured under fire, so he died very bravely.
“He was doing his job, he was trying to protect all of his other company.”
To hear the suggestion he was not on the front line was “absolutely appalling”, she said.
After making his remarks in an American TV broadcast and then speaking to the prime minister, Trump appeared to backtrack but stopped short of directly apologising for the words he used in the interview.
He wrote on social media: “The great and very brave soldiers of the United Kingdom will always be with the United States of America.
“In Afghanistan, 457 died, many were badly injured, and they were among the greatest of all warriors.”
But Bellingham said the follow-up had been “absolutely too little too late”.