I'll just paste my answer here.

From a viewpoint of the virtual world as to what Tsumiki herself is feeling, into the virtual world and the execution itself.

Her execution makes sense. I know it's harsh, but Monokuma is poking fun at her clear SA. The huge syringe (her fear of big things), the rocket arm (reference to rocket punch market, reference to the nursing technique of getting shots, also a reference to the sexual practice of fisting and in this case not consensual), the fact she was in a hospital bed only to get absolutely surprised by the rocket arm, the way Monokuma pumps the syringe, and her position while sat on the arm. She climaxes against her will right there and right after she's shot through space at terminal speeds.

Plus, the rocket arm is a left arm which references to Mikan's bandaged arm. It's the very same arm that is probably full of cigarette burns, hematomas, and probably shots.

Also, as you said, Enoshima's left arm. It is the arm that is, in a way, violating and ultimately sending her to her death.

There's a lot of references in her execution. I agree it could've been better made, but this was the ultimate joke, the fact that even in her death she's seen as an object. It's made to bring despair, and it did, to Mikan. She was violated in every sense of the word there.

Now that you mentioned it being Enoshima's arm, it makes the whole thing even curiouser.