While I agree this was a poor choice I don't think it should cost anyone their job.  Finding people who enjoy working with kids and treat them kindly isn't easy.  Reprimand both for their poor choice of words and the principals inability to look over it before it went out and file it as a normal employer does.  Likely a first strike offense.  

You reprimand discipline and move on.  This mistake didn't endanger anyone, it didn't affect any kids.  It was a message sent to adults of an elementary school geez. They admitted fault, made a correction and are talking about ways to ensure it doesn't happen again.  Angry mob of pro-marijuana folks asking for her job is ridiculous.