Ave Carlisle shivered with chills, swatted away Lucas's hand, and said, "I'm not interested, keep away from me."
What did Dr. Carlisle take her for? A confession? Flirting?
Cough, Lucas almost choked with tears in his eyes, looked at Ave Carlisle sadly, and said, "Dr. Carlisle, what I meant was... I don't have any brothers or sisters, which I regret. You're a great person, I like you a lot, please be my sister."
When Gem Atkinson first encountered Lucas in the primeval forest, Lucas was just a twelve- or thirteen-year-old boy. Considering that, she was the same age as Forsythia Brown and thus naturally younger than Ave Carlisle. It made sense for him to call Ave Carlisle 'sister'.