The child always follows the allegiance of the father. http://www.usnaturalborncitizen.com/meaningofnaturalborn.html
Harris was born Oct. 20, 1964, and her father was a citizen of Jamaica at the time of her birth.
Specifically, Chapter 2 (entitled Citizenship) of the Jamaica Constitution, Section 3C states:
Every person born outside Jamaica shall become a citizen of Jamaica –
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on the sixth day of August 1962, in the case of a person born before that date; or
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on the date of his/her birth, in the case of a person born on or after the sixth day of August 1962,
if, at that date, his/her father or mother is a citizen of Jamaica by birth, descent, or
registration by virtue of marriage to a citizen of Jamaica.
In Book I, Chapter 19, § 212, of the English translation of 1797 (p. 110) Vattel describes what is meant by the term Natural Born Citizen: The natives, or natural-born citizens, are those born in the country, of parents who are citizens.
http://www.usnaturalborncitizen.com/meaningofnaturalborn.html
It doesn't matter what that old book says. What matters is what the Constitution says and what US laws say.