A dynamic gone wrong is throttling my ability to play my character as intended, advice appreciated!
My group has been running Phandelver, leading into other adventures too. It's been a great time! Since this has been my first real dive into the Forgotten Realms as a setting, I thought I'd opt for a simple enough concept for my character, Noah. I effectively created him to be a quintessential knightly, noble paladin. Mellow, patient, but capable of taking decisive action when needed. He's more or less the Captain America of the party, and he shares some fun dynamics with the other characters. One of these characters is our warlock, Kayla.
When we started running, her player was new to D&D, so we were all very patient and tried to ensure she enjoyed herself, it paid off! She loves it, but I find myself running into a bit of a struggle with the aforementioned dynamic. See, despite everyone being the same level, Noah along with his best bud (the cleric) were established as more experienced adventurers who'd been injured and out of the game for a while, which put them in a good position to guide the fresh-faced members of the party. This led to Noah effectively taking Kayla under his wing, teaching the rookie and all that. Fast forward across many sessions, and they now effectively view one another as father and daughter.
At first, the contrast between the two was compelling, as a paladin of redemption Noah applies his peaceful philosophy to nudge Kayla away from her violent tendencies as a warlock (she was raised by a cult, trained as a weapon, ect.) and teach her why mercy and restraint are important. The problem is, she doesn't actually listen. Because her player can't resist being edgy, sooner or later, the character repeats the same wilful cruelty, killing surrendered foes, executing targets that had been taken down non-lethally, and generally earning the disapproval of the party. Time and again, Noah warns against these actions, her behaviour leads to a falling out, things begin to mend and then she does it all over again.
It's gotten to the point that Noah has told her outright that he will bring her to justice himself next time (not kill her, just arrest her) but I'm fully aware that can't actually happen, because it would mean she can't keep playing with the group anymore (she's entirely against the idea of making a new character if need be.) As a result, my paladin who's meant to be the epitome of chill is often frustrated, uselessly repeating lessons and warnings that go unheeded every single time. Is this how Obi-Wan felt? The situation is creating an entirely inaccurate image of my character and I'm really not sure how to remedy it; his oath (and morality) demands he doesn't turn a blind eye, but the need to ensure we can all continue playing together demands he take no true action.
I could really do with some advice on this. I know the immediate answer will be "talk out-of-character" but I promise we've tried. Every point brought up gets taken personally as criticism, or prompts a tantrum. Either way, it gets nowhere. If out-of-character is a process of running in circles, is there any way I can resolve this in-character?