"Hey, Sam's here! Oh... and the new girl!"
Selena's sudden appearance effectively eased the slightly awkward situation Sam was in.
The eighth grader, dressed in a white sweater, had rosy cheeks and looked quite fresh and dewy. Although she was only a year younger than Ava, the difference between them was quite noticeable due to their height and backgrounds. Ava, appearing more mature and poised, seemed more like a high school student. Despite her youthful appearance, she didn't come off as naively innocent.
Selena, on the other hand, seemed naturally clueless and childish, still shedding her youthful naivety. Girls her age seemed unaware of the instinctual competition that often exists among those of the same gender.
This kind of emotion is normal and doesn't need anyone's guidance; it happens naturally in the wild, though it's more common among males.
"This is Sam's sister, Ava. She's a grade above you."