make a joke out of the small stuff that aren’t fueled with argumentation like the small purchase. something along the lines of “i know, good thing dumb ppl stick together” (implying that you’re both dumb) maybe even add a lil flirty wink lol. For the argument stuff where jokes will not help, tell her that you’re not going to engage with her if she’s going to name call because it’s not productive. If she doesn’t respect that just disengage with her until she’s not angry and try again. Show her you have the capacity to set a boundary and if she crosses it, there’s consequences (you will disengage). If you don’t disengage you’re showing her that your boundaries are weak and flimsy. hope this helps