The 67-year-old singer-songwriter performed her song "You Can't Rule Me" during Wednesday's episode of the CBS late-night show.
Williams discussed backlash to "Man Without a Soul" during Tuesday's episode of the People Have the Power podcast. She said one fan deemed her without "compassion" after hearing the song.
"Nothing can be farther from the truth," Williams said. "The reason why I write this stuff, even though it bothers you, is because I care. To look at that and say I'm not a compassionate person because I wrote a song about Donald Trump?"
Williams said the meaning of "Man Without a Soul" goes beyond just Trump.
"It's about that type of figure, about power, about the power versus the people. It's about the people should have the power. So just plug in whoever you want to there," the singer said.
"People think I'm insulting the president of the United States. You know what? So?" she added.
Over the weekend, Williams took part in an all-star tribute to late Clash frontman Joe Strummer on what would have been his 68th birthday. Bruce Springsteen, Jeff Tweedy and other stars also performed.