Cherino is actually using a stance that I remember was taught by the US military prior to two handed shooting being popularized. The rationale was that shooting with your fist close to your heart can prevent any bullets from penetrating it.
Also, just because you shoot left handed doesn't mean you have to use your left eye to aim down the sights as well. You should use whichever eye you're dominant with.
Updated
Left-hand left-eyeLeft-handed shooting, which is rare in Kivotos.
As she uses her left hand, she uses her left eye for sights.Maybe she got lazy of removing the bullets one by one, that she just reloads a new cylinder in...She has a clenched fist, apparently to increase accuracy for herself when shooting one handed,but it could be a habit from her holding a baby rattle.
(The author is calling her a baby)