I think the reason why 13 doesn’t like guns is because she’s still reeling from all of the violence she’s gone through—hell 12 was in a prolonged battle against Cybermen which resulted in his regeneration.
It's been a while since I saw "The Doctor Falls", mostly because I just want to forget that entire series happened, but I just skimmed through it. (By the way, did you realize that Bill was a lesbian? Because I had forgotten until she mentioned it about three times unsolicited in this episode alone. lol)
Anyway, what you are saying would actually be pretty decent character development, except 12 never used a gun throughout that battle, and even explicitly said he didn't like guns. (Unlike 13 though, he allowed others, including Nardole to use them.) He did however use a shit ton of explosions, even had a child throw a grenade at the Cybermen at one point, which seems out of character in retrospect. Seeing as how one of the ways 13 has saved the day so far has included an explosion, I don't think she was changed by the battle. She just seems to be retardedly anti-gun for some reason.
As well he told her to be kind. Maybe 13 wants to atone for all the violence she went through.
I think eventually though she will pick up a gun again.
The Doctor's always been kind though. (and always made various degrees of lip service about being anti-gun for that matter)
This would be an interesting direction to take the character to be sure, but this Doctor still seems to be perfectly ok with violence as long as it's on *her* terms. Remember when she bitched at the guy who kicked the toothfairy off the bridge, and then had no problem exploding the rape sheets in the very next episode.
Or maybe she doesn’t want to corrupt her companions and create another Clara monster.
Was Clara a monster? I just thought she was a terrible character. Regardless, I can't think of any way her "corruption" was caused by guns.
TBH, the "now all guns are bad always, and nobody is allowed to use them in my presence" bullshit just seems like a personal hangup Chibby has with them. I almost want River or Captain Jack to come back just to see this doctor try to chastise them over the guns they've always used.