Hmmm. Tough issue. While I don't believe we should require teachers to directly present Santa Claus as a fact to their students (that would be almost as silly as teaching ID in biology class), I also don't think it's up to teachers to take it upon themselves to dispel this childhood myth either.

If she was worried about her own integrity (i.e. not lying to the kids), there are many creative ways she could have dodged the issue without either confirming or denying the existence of Santa.