I heard that one of your sisters met her match in the spelling bee.
I'm assuming that the underlined word is HER.
The antecedent of the underlined personal pronoun is B.) ONE.
When the antecedent is singular, the pronoun must also be in singular form. When the antecedent is plural, the pronoun must also be in plural form.
In the above sentence, even though "sisters" denote plural in number, the phrase "one of your sisters" signifies that only one and not all your sisters is being discussed. Thus, the use of singular pronoun "her".
