Fifty Years Backwards

Eirene Potter returns to the Department of Mysteries after Sirius' death because she plans on going back in time and stop him from dying. Something goes wrong, however, and she finds herself 50 years in the past, just before Tom Riddle's 5th year at Hogwarts. Determined to ignore him and find a way back to her own time, how long will it take for this plan to go awry as well? HP/TR.