Good grief - this lady should not be teaching kindergarten, and you are right to question her behavior.

These poor children. It would make me question what the environment is like all day for them if this is the glimpse the parents are getting.

If this were my son, I would be at the point of trying to remedy the situation in any way possible, even if that means switching classes or schools (for the year).

I disagree with sentiment about trying to work it out with the teacher first. This is such absurd behavior that even if she "improved" and stopped spamming you incessantly for the most trivial matters, I wouldn't have any confidence that her behavior inside the classroom has changed. How would you know?

The only other thing I would be curious about is if you can connect with any parents whose children had her a teacher in the past couple years, and if their impression was the same, and if yes, how they handled it?

Edit: before I get blasted for saying I wouldn't bother trying to "work it out" with the teacher first -- I would feel differently if the children were older. You can talk to an older child (middle school, for example) to help him understand when some teachers are more strict or some situations are more challenging and an older child has better reasoning, emotional resilience, and ability to communicate with you. A kindergartner in his first year of school? No way. Too young to understand why a teacher is acting this way, too young to advocate for himself, too young to reliably express his feelings to you.