Chaos Jackal said:When she mentions the weak person, she's talking about herself, since losing control of her powers was a sign of weakness. We already knew that the relationship between Caitlin and Darach was weird... possibly Darach came and prepared Caitlin's villa, and then they parted ways, hence the "I used to know" part and the fact that Caitlin is now a member of Unova's Elite Four.
I know she was talking about herself.
BTW, she said the "used to know" stuff in BW and the Darach coming to visit stuff in B2W2, so it doesn't make any sense.