"don't you dare get out of your parental bounds and tell children, who are not yours, about personal Christmas traditions that none of your business."
Read the letters. Someone is being asked to promote YOUR belief, not the other way around.
I did. A very simple solution was available to this teacher, but the busy-body declined to take the truly principled stand. She should have declined to read the poem and done something else instead.
I was a substitute teacher for many years and routinely had to change up the lesson plans for various reasons, as all subs do on occasions. This teacher is using this cause to be a martyr, IMO. She passed on the sensible soloution and has found herself neck deep in a controversy that she alone created.
It is part of a school curriculum, it is not a single person telling her to teach it...if she can't cope with following the curriculum, then she needs to quit!