Use "Analyze" to discover the real Shizu and focus on her, she has better stats than her clones,
If you try to do the labirynth and you have problem with lady-snake-but-werewolf-wanna-be, then you can just cheat her fights by saving before atempting to flee. If you have decent lvl going in, it should let you win easy.
( If they patched and now you can't flee from those battles then welp. You gotta go grind some lvls boyo)
For that I propose self-made trips with tons of mimics and some proper Demon (s)Layer.