sometimes killing them with kindness works but rarely.
Allow me to tell a story. Used to play in a pool league from a tiny hole in the wall country bar. Rough place, rough men, the regulars were safe but you never knew what kind of trash would come in looking to start a brawl. A favorite way was to cheat at the pool table or to be rude playing.
When practicing one night the system was to set your set of quarters in line with the others in front of you, everyone kept track of who was next. So I'm next and this young punk swaggers in and lays down two quarters at the tail end of a line of maybe five sets of quarters.
Winner holds the table, loser sits down at the end of the game and the next person in line plays. Except punk man/child steps up knowing he is jumping line at least five people and racks the balls. Everyone looks at me, knowing I'm next. I just wink at them and motion to stay cool. The guy is a good player and wins the table, I'm up next.
I rack the balls very tight, he gets a poor break and starts swearing. Me, I am not the best shot in the league but I am an expert at position playing, where you take your shot and sink a ball or not, you leave the ball in the worst possible location for your opponent. Hiding behind other balls, making it hard for him to make the next shot.
Mr punk boy is pissed as I slowly sink a couple of balls, then "miss" a shot, leaving my ball blocking the only pocket he had a shot at. He slams a shot, scattering balls all over, a very poor way to play, uncontrolled, risky.
Now usually you play friendly games, you hide your light under a basket so to speak. Play just hard enough to win but not hard enough to give away your true talents or piss people off. You show your stuff at the tournaments, not before. But not this time, punk boy had scattered the balls around the table and I start slamming the rest of my balls into the pockets, never leaving him a shot in case I missed a shot. Perfect position, with the cue ball never stopping where he had a shot but I always had an easy shot. I ran the table, dropped the eight ball. And just stood up and looked at him. Everyone is looking at him. They know I am pissed off and just wiped the floor with him. The dude is humiliated. He nods, walks out the door. He was an *ss, came in looking for a fight, and learned he provoked his way into a butt whoopin. Now that is how most men roll. This Karen in the OP's story, different kind of person.
Moral of the story. You don't stop bullies by turning the other cheek. You have to humiliate them, give it to them worse than they gave to you or others. You show grace, give them the turn, then play with them, then wipe the floor with them, and they will usually acknowledge their defeat and leave with what dignity they had left.
Humiliate them from the high ground. Anything else doesn't stop them. People know when they are being jerks. Call them out, let Jesus do the forgiving at another time and another place.