Cindy Busby is Karen. No, that's really it down to the hair cut.
The premise is that she leaves her kid for three days with a nanny. Only the nanny is (insert title here) and from that point onwards nobody cares about the plot device, it's just the world against Karen and she must fight them all to prove how amazing she is. So what if she physically assaults random people and a cop, so what if she breaks in to another person's house.
That's fine and you're wrong for questioning her! SHE IS KAREN AND HAS EVERY RIGHT TO YELL HER LUNGS AT YOU! Unless you yell back then she'll back off like a proper Karen does, manners after all.
The movie does nothing to shift you to her side which is impressive consider "a mother scared for her child" is the easiest sell in the world. Here though the child doesn't matter. Just Karen does and her indignation.
There is also some deep seated white entitlement and racism going on in the background of a few scenes. I want to think that it was on purpose to show case her as a bad person but I don't think the movie is that smart. Avoid it, not worth your time.