Ok so maybe I’m reading too far into this, but, the first rule of using any kind of gun is that the finger only goes over the trigger when a person intends to shoot. I’ve had it drilled into me that even while aiming a gun my index finger goes on the space above the trigger. Absolutely, under no circumstances, does a person put their finger on the trigger until they’re ready to pull it.
Which means in this scene, Riza completely intends to shoot Roy. She didn’t put up and aim her gun for show. She’s about to pull the trigger and kill him.
you are absolutely not reading too far into it.
if you go through other scenes where characters are holding guns, the animators have in fact shown them practicing trigger discipline when they’re not (or no longer) ready to shoot.
here we see riza ready her trigger finger when she aims at scar,
only to disengage the moment edward elbows her out of the way:
here she has her trigger finger ready for gluttony, but once she identified that she was aiming her other gun at allies, she disengaged:
i will say that i personally think there are many moments where characters have their fingers on the trigger when they really shouldn’t yet (including the above screenshot of edward elbowing riza, in my opinion). but, these are animators not gun experts, and the characters are in fact aiming at targets they’re willing to destroy in every instance of what i’d argue is poor trigger discipline.
in conclusion, for riza to be aiming at roy with her finger on the trigger when we have numerous instances of characters holding guns with proper trigger discipline is 100% intentional, and appears in the manga the same way:
I am Silver Tongue, I am an artist. I have many characters and you can check out my art in the art tag. I occasionally practice witchcraft though I don't do anything too complicated. I am girl 2 and don't know what else to put here.