(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?
Because this is Invincible, not Captain Marvel.
Making a one dimensional, unstoppable superhero who’s only weakness is not believing in herself is bad writing.