Seems a bit excessive on her part, especially with the "Anger Management" reference. Obviously we don't have her side of the story... but it seems that with the exception of your snarky comment, you were pretty rational.

I'd drop them a line, and be as upfront as you are now. It's entirely possible that this was a misunderstanding/miscommunication on both your and her part - in which case, no harm, no foul.

However, if this is a pattern of hers, she'll probably have other letters in her file, and one more letter might make a difference. It could be that you caught her on a relatively "good" day, and the next time she might have reamed you a new one. Not good for her or for NW.