Oh no, not me obsessing over the end of RWBY 9x03! Not me looking at Neo's Semblance activating unconsciously and the implications of what it does!!! Not me especially obsessing over seven seconds of it becuase shipper brain!!!!!
We know thanks to Roman Holiday that Neo's Semblance sometimes acts outside of her conscious control. (This isn't exclusive to her of course, but the specific precedent still exists.) She's just found herself in a strange land, with the knowledge that Ruby is alive and here somewhere too; she's still very vengeance-oriented towards her, maybe obsessively so, and her Semblance outs her single-minded focus by making her take on Ruby's appearance.
So, strange land. Fueled more by emotion instead of thought. Then an unknown threat shows up, and as soon as she picks up on it, her Semblance turns her into Cinder instead. And let's pick the implications of that apart, shall we?
Neo's not thinking so much as feeling right now. There's an unknown threat, so her fight-or-flight kicks in, and since this is a very pissed-off Neo, she defaults to fight immediately. In a strange place with an unknown danger, you want to make yourself look powerful and intimidating to prove you're a more dangerous threat than the thing coming after you. In other words, while she may not consciously be intimidated by Cinder (see the "You're being stubborn and stupid" looks when Cinder decided to sneak out against Salem's orders, and the fact that she decided to blackmail/threaten her with the lamp), an unconscious part of her knows that Cinder is powerful and intimidating; therefore, when she notices a threat, she takes the appearance of Cinder when she turns to look at it. Out of all the people she's met (Salem, for example), her Semblance picks Cinder. That's just so deeply fascinating to me. (Yes this is the seven particular seconds, and yes I ship these two very hard, fucking sue me.)
And then, when faced with the strange monster that's the Jabberwalker, she turns back into herself to fight, which as a deactivation of her Semblance after she acts, is likely a conscious choice. But that's not all. Her Semblance goes rogue again and makes a small army of herself to overwhelm the thing. She ends up not even deigning to fight it with her real self, but sics her copies on it instead. Now that she's seen it, it turns out it's not even worth her effort. There's only one target down here she wants to put her energy into killing: Ruby.
I honestly fucking love Neo, especially now that her backstory has been revealed, and my brain loves overanalyzing characters I love.