She could potentially wield two weapons at once, though that would be ridiculously difficult to implement.

Two weapons would also make short work of the bosses, I would assume...

If I'm not mistaken, Randolf once ASM hacked the Blade so that two of them are thrown (in opposite directions), though throwing the Blade up or down was impossible.
And the Level 1 Nemesis created experience making it possible to use that to level up with ease (until you accidentally leveled it up to level 2).

Can't remember what mod that was, however...

First off, who's Randolf?
Secondly, that's awesome

But yeah, she can wield two weapons at once if she felt like it. (Which she doesn't - she feels that using two weapons at the same time would lessen her accuracy.)

That's probably a logical reason, in-universe...

Aside from Serenity, however, another NPC is ambidextrous, and it has two guns at the same time. It's a common enemy, though. It appears in the Servant Quarters area. (Or some other area. Not really sure just yet.)

I almost misread that as "a bonus boss with multiple forms".