No, the word was not sexed in Japanese.
Japanese is not English. Many words in Japanese used to refer to people are not explicitly gendered, but rather their gender is implied through context. The meaning in Japanese in context (series explicitly about girls, comment explicitly about a girl) is not 'chairperson', so a translation to English shouldn't present it as such either.
For comparison, sometimes Japanese sentences also omit pronouns where we would use them in English in a sentence, but English translations add the implied pronouns so that it means the same thing. It would be equally incorrect to leave them out altogether (broken sentence in English) or put 'they' everywhere (different meaning) and justify it with "well the original text didn't
explicitly say he or she".