Note:
I've been experimenting with various Helminth abilities to replace her Mind Control. It's a versatile spot, because you could use an ability that benefits from high range, duration, or strength, or any or all of those. Basically anything.

Pillage would work, of course, and is a popular choice for [Nyx], but I use Pillage a lot and wanted to try something different.

My first attempt was to put Shooting Gallery in there. That worked very well, and really improved survivability, BUT ... it worked too well, and left me never using her 3 or 4, because enemies weren't attacking me.

Then, I put '[Rage]' in there (from Rest and [Rage]), thinking that it would mesh really well with the other abilities. It does. You enrage enemies, lowering their defenses a lot, letting them kill each other more easily when you use your 3, or making them more vulnerable to your 4 nuke. It fits her theme a lot, and I'd recommend [Rage] for sure, but it feels kind of meh to me, so I'm still trying other options.

I recently put Ensnare there for general utility, and it's fine, but it doesn't synergize with the other abilities. I also intend to try Pull, and just use it for assisting melee and causing general calamity. You could also put Smite to increase her 'making enemies fight each other' even more, or Eclipse to have a general buff that you cast and forget.