"I know what you've done, but you forget I also know what you've yet to do."

Anakin Skywalker died in the Light. Leia had been skeptical, but Luke had firmly believed it and Rey chose to latch onto that belief herself in the absence of anyone who could tell the unbiased truth. However, it raises a question she hadn't considered fully until just now -- if perhaps a different ending were possible for Vader. If there could be a world in which he walked away from that final conflict. If Kylo could grow up knowing his grandfather from the start.

It's something to consider. There won't be any way to know unless she goes home to find everything changed, and maybe that's for the best.

"Master Kenobi cares for you. I can't imagine he'd seek to harm you here without a pressing need to do so."

That much had been obvious since Obi-Wan had kept Vader to recover in his hut. She didn't know the entirety of what had passed between them over the years, but it was clear that they weren't enemies here.