The 'Mind Ripper' is actually the Zatarian equivalent of a noogie
Ralen's the first Zatarian to attend the Academy, and he frequently tells others that they don't understand his people, so why not take advantage of that for purposes of intimidation? Jax is a human/Zatarian hybrid
That would explain both how she could be resistant to a plague that Zatarians are immune to, and why her uncle is convinced she's a threat to Earth.