Sure, even if that’s he case, doesn’t mean she has to go melee against him.
She could just as easily shoot at his legs or ankle to disable him. And if she didn’t over do it, he can be disabled or disarmed without losing his limbs, just functions of it perhaps, not too far from the results of the melee.
Or, alternatively, I’m surprised they don’t have a space age stun gun or something ranged and not lethal to apprehend criminals.
Being seen in battle is probably part of the calculus for the battle's strategic and political objectives.
Showing off to both allies and enemies.
Also Selina is a bit of a blood knight, as seen previously, so her desire to have a close-combat fight should also be factored in.
On top of that, since they were told that an Artifact would be on the field, she probably engaged in close combat to draw out its use, and to see it in action.
Knowing the extent to which Artifacts are able to stand up against Imperial technology is very important information, especially given that Alan and Iris don't know when they might have to face another one.
As for not having non-lethal weapons, they might have something from their shipboard MPs' weapons locker, unless that was also destroyed during the accident. But the pulse rifle appears to be able to function in a non-lethal capacity with its guided shot mode.
