Yes, I think this needs to be viewed through a behavioural lens. There may well be some anxiety and perfectionism fueling the fire, and that needs to be addressed, but she foremost needs to understand that her chosen manner of expressing herself is unacceptable.
A social story might help. Give her the scaffolding she needs to see what appropriate behaviour looks like when she faces common challenges, and provide a reward for following your prescribed set of steps. Ensure there are meaningful consequences to her for any problem behaviour every time it surfaces. If she misses a step or fails while sincerely trying, that's not punishable, but pitching a fit or being rude is.
If it's any consolation, my DS has been going through a boundary testing phase lately, and I've had to leverage social stories. They work. Tonight we had an hour of parental propaganda after a challenging episode at the dinner table, followed by writing our own social story together. This may not apply well to others' children, but I find acting out the offending behaviour myself or responding the way a peer would helps DS see why a course of action is problematic. Parents are the gentlest teachers; let her learn this lesson with you and not someone else.
