Keeping Athena safe, at all costs, was her top priority. She agreed with Pansy, that Thoros wouldn’t hesitate to kill Theo once he was able, and that Theo would claim Athena as his heir the moment he met her. With Theo gone, Thoros would set his sights on Hermione and end her life just as quickly. As an orphan, Athena would be handed over to her paternal grandfather, leaving her at the mercy of Thoros Nott. Even if he couldn’t kill her, he would torture her the same way he had Theo, and there was no universe where Hermione would allow that to happen.