(no comic spoilers please)
Since she can apparently turn anything into anything (as long as it’s not human/animal matter), why doesn’t she immediately turn all her enemies’ equipment into sand?
The Flaxans’ guns? Sand. Killcannon’s kill-cannon? Sand. Doc Seismic’s gauntlets? Sand.
She can apparently manipulate matter attached to her own person (e.g. changing her outfit), so why not others’?
Is there an in-universe reason for this, or is it a writing issue?
The answer is that Eve’s powers are limited first and foremost by the mental block discussed in the special, and second by her own reaction time and imagination. Third, excessive use of her powers has been shown to seriously fatigue her. The little energy discs around her hands likely take far less energy than would be needed to transmute an entire legion’s worth of rifles into sand.
If you read the comics, she does come into her own a bit, and builds up her ceiling just like you’d expect for a superhero show. But we’re still early days for Eve. Can’t make her Dr. Manhattan overnight. She and Mark need to build over time. If Goku could access all 15 levels of super Saiyan (or however many there are now) by episode 10, why watch the rest of Dragonball?
TL;DR let her cook
Power of plot.
A superhero’s power in any given fight is exactly at the levels the authors need it for their current narative.
It doesn’t matter what the hero was capable of just one scene earlier or after.
Also 99.9% of the authors don’t understand the physics involved in feats that are just added because they’re cool and the implications these should have (but just don’t)