Williamson was raised upper-middle-class in Conservative Judaism. Her family attended Congregation Beth Yeshurun, which was later damaged by Hurricane Harvey. She learned about world religions and social justice at home, but first became interested in speaking from the pulpit on social matters when she saw her rabbi speak against the Vietnam War. Her family also traveled internationally during the summers when she was a child. She has said that it was through travel that she "had an experience, at a young age, that people are the same everywhere."