Haunted by the ghost of her brother, Alison Oliver's depressed Portia is on a path to self-destruction In 1994, the National Maternity Hospital in Dublin commissioned Marina Carr to write a play to celebrate its centenary. She walked the wards, met the new mothers, and wrote in a hospital study. Who knows what the commissioners were expecting, maybe something more upbeat, but what they got was a harrowing portrait of…