Answering the question above…
That is a fair observation that I didn’t think about in that much detail, but I figured it made enough sense in the “Maki shoots people through the window” -theory, as the arrows were poisoned and thus a shot to the arm would be equally lethal as a direct hit somewhere else. Kaito sticking his hand through the window to give her the remote would give her the perfect opportunity to shoot him, as she couldn’t shoot before Kaito gives him the remote, since that would probably make Kaito not give her the remote at all. She could’ve shot Kaito after he had given the remote, but why wait when she’d have the perfect opportunity while Kaito’s arm was outside the window.
However, the Exisal being inside suggested that the whole window shooting scenario never really happened, which makes Kaito being shot in the arm a bit less likely. However, it is still reasonable. If Maki drove the Exisal to the hangar and then shot Kokichi, and this was planned by Kaito and Maki in advance, Kaito would lower his guard. Then, Maki could just take whatever opportunity she would get to shoot Kaito. She wouldn’t shoot him from the front, as that could alert Kaito and potentially allow him to react. So, she waited a moment, and shot him when Kaito was facing to the side, hitting him in the arm. Sure, she could’ve waited until she has a chance to hit him square in the back, but it’s not that unreasonable to take an opportunity to hit him in the arm.
Also, it is possible she wanted to hit Kaito in the arm in order for his coat sleeve sticking from the press to have a bloody hole in it, making it clear that Kaito was attacked.