Having Rey kill her parents would fill the dramatic void left by her evil heritage, shown through visions and maybe even Rey saying to Finn “I killed my mother… and my father.”
“I killed my mother… and my father” That’s how it is in the released TROS: Resurgence Workprint. There is dialogue of Rey whispering the word “I” in TLJ so it can be blended perfectly. See rough clips:
Hangar confrontation, “You wanted your parents dead…”
https://youtu.be/tA2L3QHZTCw
With Finn, “I killed my mother…”
https://youtu.be/oxi7afxLBu8