Looking back, I think the animalistic behaviour of the DLF Rats here gives a clue to the practical reasons (aside from whatever psychoanalytic shit the Prophet is pulling) behind the form of the UAE Assault Girls - it's so that mind corruption by default tends to pacify the human operator for easy elimination. If they looked like more conventional militaristic mecha, mind corruption would tend to straightforwardly drive the pilot into being an unthinking killer - while brainwashing them into thinking they're a young girl will temporarily render them less violent, at least until corruption gets bad enough for their bodies to start warping.
The DLF, as less centralized guerilla cells who aren't as beholden to civilian leadership, simply mock their units up as animalistic monsters and drive the ones showing more corruption (and thereby unhinged rage) onto suicide bombing charges.
