Thanks so much! I'm really glad you've been enjoying the game :)
From what I've discussed with other players on Discord, the most consistent setup for Nix seems to be Violetheart Pendant, Regen Sigil and Ironhide Greaves/Snowboots.
Few tips:
Collect every Quartz you can in the Subsoil and Gravel layers. As long as you have shield stacks, Nix is immune to Gravel damage.
Only go for restore cells and Quartz that are reasonably close in the Underbark and Sporegrove layers. Try to balance your stamina and shield stacks.
It's also very important to carry shield stacks into the Blightvein layer since they reduce the damage from Toxin detonations.
Save as many shield stacks as you can for Shimmera and Umbra as those biomes can drain lots of stamina due to their hardness.
That's about all the advice I have for Nix. She's definitely the toughest turtle to get to Deepwater with and even with a good strategy, most of the time it comes down to rng as well.
Thanks again for the kind words! Good luck!