She works for the Ministry of Magic, in the Improper Use of Magic Department. She sends howlers and letters to young wizards who have broken the law of not using the magic outside Hogwarts. She wrote to Harry twice. The first time was in the summer before his second year when they though Harry performed the Hover Charm instead of Dobby. Then in the summer before Harry's fifth year she wrote to him because he cast a patronous charm to defend Dudley and himself from Dementors.In the seventh book, the trio catch and erase her memories to get some of her hair. Hermione Granger drinks Polyjuice Potion with these hair and she gets into the Ministry with her appearance. Then, Dolores Umbridge takes her as secretary for the Commission of Register for Muggle-borns judgment to Mary Elizabeth Cattermole. She steals the locket from Umbridge, but Harry arrives and messes up everything, helping the Cattermoles escape.. Presumably, the authentic Hopkirk continued working at the Ministry after the war.