The Birth: The Silver Banshee first wailed her way through Superman:Action Comics #595 in December 1987. The isle that stood in the North Channel midway Ireland and Scotland had been in the McDougal family since the days of the old religon. They were a strong and brave lot, the McDougals. And to prove themselves worthy of the McDougal name, the first born must decend into the sacred grotto of the isle beneath Castle Broen and confront the forces imprisoned there. This time, the first born was a girl; Siobhan. Though no woman had ever led the clan, Siobhan insisted on her so called birth-right. She stole the ritual tools and called forth the spirits of the grotto. Unfortunately, she was distracted in mid-ritual by her brother Bevan who had been sent down to subdue his sister, and thus seized by mystic forces and banished into an infernal netherworld. An ancient crone, taking pity on young Siobhan, freed her and allowed her to return to earth as the Silver Banshee.

The Alter Ego: The fisrt born of Seamus' brother Garret McDougal, was a fine and fair girl named Siobhan (pronounced Shee-Voughn). A restless tomboy at heart, she travelled out into the world. She returned after six years when her father died. It was then that she sought her birth right and by a misfortune of fate was transformed into the Silver Banshee.

The Legend: Siobhan hailed from Castle Broen, located on an isle which had been in her family for generations. The old crone returned her to earth as the Silver Banshee but before she could have her revenge on her brother Bevan and her uncle Seamus she had to retrieve the book which chronicled her McDougal's history. Seamus had shipped it out of the country but the Silver Banshee was able to track it down to Metropolis. She readily killed anyone who got in her way of finding the book. This made it clear that she had failed he Clan and so the book was destroyed by the Crone.
The Silver Banshee's main weapon was her deadly voice which was lethal when used in it's flat pitch. When highly decomposed bodies turned up of people who were known to be hail and hearty the day before their death, the cops knew that the Silver Banshee was back in town. Captain Maggie Sawyer (See the S.C.U files) had brushes twice with the Silver Banshee and so did J'onn J'onzz (See The Martian Manhunter). Her power to kill with her voice was somehow cued visually, a fact which enabled Clark Kent, Superman and J'onn J'onzz to defeat her. The Banshee's high pitched wail enabled her to somehow teleport out of sticky situations, due to which she was never caught.
When the ancient Crone destroyed Castle Broen along with the McDougal isle she was believed to be dead. But she turned up once again, this time in league with Blaze, a witch of the underworld. Nevertheless, Superman was able to defeat the duo.

Action Comics #595