Another Charlotte Robespierre who has the exact same three first names as Charlotte, admits to having lived with the Duplays and having feuded with them and her two brothers, an older and a younger, just like Charlotte, to interacting with Guffroy and therefore causing her brothers' further displeasure, just like Charlotte, and to being found using Charlotte (and Maximilien and Augustin)'s mother's maiden name? Somehow, I don't think that's likely. People do lie about their age and this is especially common for unmarried women in a period when never marrying was considered the worst possible fate for a woman.