Cheyenne is a direct descendant of the Vault Dweller, Vault 13's Hero who stepped out into the wastes to replace the Vault's broken water chip, his journey eventually lead to him finding and destroying the source of a recent mutant uprising and saving California from certain doom.
The Vault Dweller didn't receive much by way of praise for their actions. Upon returning to the Vault, he was confronted by the Overseer, who told him that his time out in the wastes had changed him, that he was a threat to the entire Vault. With that, he turned the Vault Dweller away, sending him back out into the Wastes, presumably to die...
However, the Vault Dweller's heroic deeds seemed inspirational to many of his fellow vault dwellers, who took off after him. Upon finding him, he lead them further out into the wastes, where he proceeded to show them how to survive out in the wastes and eventually helped them form a settlement. One of the followers was Pat, the love of the Vault Dweller's life, the two of them settled down, married and had a child together, a child who would later go on to become Cheyenne's mother.
Cheyenne was born forty years later, by this time, the settlement had become a lot more tribal than it initially was. Many superstitions existed within its walls and the folks there adopted the 'simple life.' When she was twenty, she was elected to go out into the Wasteland and save its people from the decay and stagnation that was slowly claiming it.
Cheyenne is a rather chipper and charismatic figure, who wishes to help people whenever she can. Her cousin said that her 'pointy nose' was ideal for poking itself into other people's trouble. Though Cheyenne rarely takes things seriously, it is obvious that she deeply cares about those who need her help, especially her own people.
In Being the Chosen the shock of seeing what has become of her family, friends and community puts her into a depressed slump, in which she is openly hostile to anyone who tries to snap her out of it, going as far as to point a gun at Myron. Her friends make a note of how uncharacteristic this is of her, due to her usual aloof , facetious, nature.