"That one is actually the easiest to explain," Melissa says. Hence why it was first, presumably. "If you're not loud, how are people supposed to know that you're there to help?" she asks, explaining the first part.
"If you're not friendly, how are people supposed to know you're not a villain?"
And then, finishing out the symmetry of the statements, she says one last question. "And if you're not bombastic, how are people supposed to know that you're a hero?"
"That's how every hero acts."
In her own mind, she's kind-of got a good point. If you lack one of those three traits, then you won't be able to do any hero-ing. Rude, quiet, and antisocial girls like her obviously can't be heroic. At least, that's what she thinks.