Isabel Brown was the younger sister of Rose Brown.
Background
Season 6
Isabel was close with her sister Rose. Rose however, was accidentally killed by her co-workers after they pulled a prank on her. Rose came back as a ghost in order to enact revenge on each of the men responsible.
Sam Winchester found out where Rose was buried, but salting and burning the corpse didn't prevent Rose's killing spree. Sam contacted Rose's sister Isabel and asked about Rose. When Sam asked if Isabel had any of Rose's remains, Isabel said she had received one of Rose's kidneys.
When Rose began pursuing Sam and Dean Winchester, Isabel was accidentally killed by a glass shard from The Impala when the vehicle struck a wall. Her death caused much grief for Rose, who apologized for what she did and with Isabel's death, Rose was also put to rest.