They weren't really bad or mean girls, just misguided by a bad influence (Penelope). They'd probably be Betty's friends if it wasn't for her.
I could picture them discovering Betty's secret, but promising to keep quiet about it, and eventually becoming Galactic Guardian cadets themselves.
They are just hangers-on. They don't do anything except follow Penelope and laugh at her jibes and putdowns of Betty.
i don't think they are pretending to be mean just to please Penelope as that would be too subtle for the target sudience.
my thought is that they are attracted to Penelope's wealth and social status and hope to gain from it. They sre not nice people so would not make Galactic Guardians themselves. I don't think Betty would get along with them either.