In Star Wars: The Force Awakens, in the scene where a First Order officer informs Kylo Ren that they couldn't retrive BB8 from Jakku, Kylo Ren force grips him and asks him angrily "What girl?". Meaning that he knew her, and was afraid.
KYLO REN: Anything else?
Mitaka hates to say the following, but:
LIEUTENANT MITAKA: The two were accompanied by a girl.
Ren reaches out -- Mitaka is suddenly, violently PULLED TOWARD REN, into his black glove:
KYLO REN: What girl?
This scene was a source for fan theories that Rey was Luke's daughter, trained together with other students (including Kylo) in his new Academy. (So Kylo Ren knew her from there.)
After The Last Jedi, we found out
that Rey isn't a Skywalker and her parents were scavengers too.
So how could Kylo Ren know her before the events of episode 7, and even be afraid of her?
Why would Lieutenant Mitaka hate to say that a random girl is with them? What does he know that we don't know?