Irene was a cousin of Amy Farrah Fowler.
In "The Isolation Permutation", Amy said that 12 years ago Irene died with the rest of her bridal party due to a kerosene heater accident just prior to her wedding, releasing carbon monoxide. The bridal dresses were still available to Bernadette for her wedding at no charge. Bernadette didn't want to use the dresses left by dead people and Penny didn't like the style. Amy accepted that, but was hoping some good would have come out of her family's tragedy.