She simply couldn't let anyone know Bellatrix was alive or she'd be dragged off back to Azkaban and how would Hermione ever get her satisfaction then? The Dementors had been scattered and driven off while, Kingsley, who most were already treating as the next Minister for Magic, had made it clear the services of such creatures would no longer be employed by the Ministry. So Bellatrix wouldn't face the dementor's kiss if the Ministry took her but she would be still most likely locked up again in the deepest darkest cell possible far beyond Hermione's reach.