Reagan struggled to convince Thatcher to agree to allow the 1986 U.S. raid on Libya to be launched from British bases. She was similarly troubled by the 1983 American invasion of Grenada.
"Mrs. Thatcher was heard to expostulate, not once, but many times 'How could (Reagan) do it without telling the Queen, i.e. without telling me so that I could inform the head of the commonwealth,'" Ingham said.
She gave the president a friendly "ear-bashing" over that and his attempt to make a nuclear disarmament deal with Gorbachev at Rejkyavik, Iceland, in 1986.
On the day of Reagan's funeral, Thatcher sat behind the former president's son, Ronald Prescott Reagan, looking sadly on as he comforted his mother, Nancy.
"Ronnie and I knew her as a dear and trusted friend," Mrs. Reagan said on Monday in a statement. "I will miss her."