According to her responses to the New York Times, Harris supports single payer. She would still support private insurance for supplemental coverage. Her website has a page on her health care position as well.
Harris is pro-choice.
She is a co-sponsor of the Green New Deal resolution that Alexandria Ocasio-Cortez (AOC) and Ed Markey introduced in their respective chambers.
According to her website she supports campaign finance reform but has not stated if she would break up monopolies.