Looks like more of a fear of being abandoned. My guess is that due to her popularity, some "friends" got jealous of her and started bullying her. Started off small at first, a rude remark here , a little shove there, just trying to get some frustration out, til they were all out picking on here...
I'm going to be really fricking mad if this ends how I think it will, the entire thing being a misunderstanding. The real person who saved the older sister being the older brother, and the younger sister was helped by the MC in some way but thought it was the older one. And then they swap and...
Definitely a Glow up. Homie went from Gag to Gruff, from Poledancer to Pole Slider (Fireman), Shirley Temple to Jack Daniels, Cosmopolitan to Cosmos' repopulation