Kate Kane

Kate Kane (full first name: Katherine) (b. 1972) (d. 1986) was the daughter of Jacob and Gabrielle Kane, the twin sister of Elizabeth Kane, niece of Thomas and Martha (née Kane) Wayne, and the first cousin of Bruce Wayne. Two years after her mother and sister were killed, Kate died from cancer, with her father following after her from alcoholism eight years later.
Alongside her paternal aunt and uncle, Kate makes a brief appearance during the little man who wasn't there. It can be inferred from how she speaks in this and her being the namesake of his daughter, Bea Wayne, that she and Bruce were close before her death.