The Democratic candidate said she had wanted to "curl up with a good book and never leave the house again. But in a speech at a children's charity she urged the audience to fight for American values and "never give up."
Mrs Clinton won the popular vote but was beaten to the presidency in the all-important US electoral college.
"Now I will admit coming here tonight wasn't the easiest thing for me," she said as she was honoured by the Children's Defense Fund.
She continued: "I know many of you are deeply disappointed about the results of the election. I am, too, more than I can ever express.
"I know this isn't easy. I know that over the past week a lot of people have asked themselves whether America is the country we thought it was.
There was little ceremony and no sign of security for the former presidential candidate who is known simply as "Hillary" in this circle of friends.
The audience were on their feet and chanting her name as she took to the podium. When she talked about her disappointment, murmurs of agreement spread through the room in waves.
That murmur grew louder as she urged those listening not to lose heart - this was an emotional plea for action.
The event was entitled Beat the Odds, which offers hope for some of America's most underprivileged children and celebrates their achievements.