The problem with your answer is that you require an unreasonably large degree of knowledge of what was going on in the girl's head, and in Rittenhouse's.

To me, the basic answer is really simple.

Self-defense means that if someone is trying to do you grievious harm, you are permitted to stop them even at the cost of the attacker's life.

It's not okay to rape.

Not if she's carrying a knife, not if you've had sex with her before, not if she looks like "the type", not if she's alone with no-one to help her and no way to recognize you. Not if she's wearing something sexy. Not if she's naked. Not if she stole your wallet. Not if she belittles your manhood. Not if she's slept with fifty guys. Not if she was your girlfriend and was in the club cheating on you. Not if the victim is actually male. Not if they're trans. Not if they dumped their drink on your pants. It just doesn't matter! There are other ways to deal with any aspect of their behavior that might be a problem. Rape is not okay.

And because it is not okay to rape, it is okay for the victim to defend themselves using what means they have available, including whatever they might have brought specifically for that purpose, whether or not the thing they brought was actually allowed where they brought it. If she brought a switchblade, which is illegal in the state, into a club where weapons are forbidden, precisely because she thought it was likely she'd be attacked, it's still self-defense.

Because the attacker didn't have to do that. The attacker was terribly in the wrong, and the attacker's victim deserves a chance to save themselves.

(The victim can still be charged with illegal possession of a weapon, if it was illegal. Just not murder.)

It's also not okay to murder, or to inflict grievous bodily harm.

It doesn't matter if the person is male or female, black or white, old or young, bald or with a beehive, carrying nothing or a rifle, is polite or swearing at you non-stop. It doesn't matter if they're racist, doesn't matter if they think Star Wars Episode IX is the best movie ever. It just doesn't matter! There are other ways to deal with all of that. Murder and assault are still wrong.

And because it's not okay to murder or inflict grievous bodily harm, it is okay for the victim to defend themselves using what means they have available.

Because the attacker didn't have to do that. The attacker was terribly in the wrong, and the attacker's victim deserves a chance to save themselves.

Why should it matter even if Rittenhouse had happened to be on a self-imposed mission to murder two hundred black protestors? He didn't act on it. Nobody else knew he had that planned. (In this hypothetical.)

The attackers didn't have to attack. There was no imminent threat.

The only way you can justify the attackers having the right to attack is if...they were attacking in self-defense!

And if you compare the victims' actions to Rittenhouse's, theirs are in every case by far the more aggressive. (Less effective, but more aggressive.)

Now, you could have laws about gun ownership so that it would be very likely that there would have been zero rather than three guns involved in this incident, like a lot of other states already have, but not Wisconsin. You could have much tougher laws about curfew, much more robust policing + deployment of national guard during riots, and so on. That might be "not insane", as compared to the current situation which is, well, yeah.

It's exactly like the original author said, though: if you don't want this outcome, change the laws.

Also, might be a good idea to point out, repeatedly, how two extra-judicial killings is not part of our ideal for how to handle rioters. That's the kind of stuff we blast third-world totalitarian dictatorships for doing when they have riots.