Beth Sanchez was the original daughter of the titular Rick Sanchez from Dimension C-137. She lived a childhood similar to other versions of Beth, where she had Rick make inventions for her such as Froopyland, but most likely had happier times, since her parents had a happy marriage, unlike other Beths whose parent's had failing marriages. But this Beth's life was cut short when an alternate Rick, Rick Prime, sent a bomb to kill her and Diane Sanchez after her father chose family over science.
Beth and Diane's deaths led Rick to invent interdimensional travel and try to hunt down Rick Prime, and eventually he helped build the citadel. He traveled to Rick Prime's original dimension and moved in with the Beth that Rick Prime had abandoned.
The events of her death were first seen in a memory projection in "The Rickshank Rickdemption". This memory was stated by Rick to be "totally fabricated", but in "Rickternal Friendshine of the Spotless Mort" and "Rickmurai Jack", it was confirmed to be mostly real, except for what happened immediately after Beth's death.