Okay, how about this then:

Luke: “Because you’re a Palpatine. Leia had sensed your pull to the dark side.”

Rey: “She didn’t tell me.”

Luke: "Leia knew your strength.”

Rey: “She still trained me.” (Rey mistaking mental fortitude for physical strength)

Luke: “Your choices define you. Your heart. Rey, some things are stronger than blood. Confronting fear is the destiny of a Jedi…”

This allows you to recontextualize the conversation between Rey and Leia at the beginning. Leia did know exactly what was going on with Rey, but she didn’t think she needed to say it aloud.