...given her history so far, she is actually more likely to help the girl get her revenge.
If the hypothetical girl's parents are murdered I would hope Riri would take up the cause and try to find a way to expose the murderous cops. Whether their daughter becomes a mass murderer herself seems almost irrelevant. The murder of the parents and unraveling the conspiracy where Cops are covering up 2 executions would seem more important than whether their teenage daughter becomes Riri's new arch nemesis.
Who said anything about a conspiracy? The way I envisioned it is, the cops murder them in broad daylight, make up a paper-thin excuse about fearing for their lives, and that's enough to convince the jurors that they are innocent.