Jamaica became independent in 1962. India in 1947. Harris was born in 1964. So whatever else she is, it’s unlikely that she is a British citizen. She could not apply for a British passport since neither her parents nor her grandparents were residents of the UK home islands.
Donald Harris held a British passport in late 1959, the terms of which stated it was good for five years. Was Kamala born while Donald Harris was on a student visa to the USA as a British subject (although Jamaica itself received independence in 1962)? The answers are within official archives.