WHO IS ISOBEL O'FLAHERTY?

It's the first day of term 1984. Minerva is calling the new students to be sorted to their houses when she comes across a name that seems to disturb her: Isobel O'Flaherty. She looks at Dumbledore for answers but he ignores her. Only Severus seem to notice the scene from his seat. Who is this girl? Why does her name make Minerva tearful? R/w