Current Employer Calls New Employer and gives false information.

My daughter in law is a teacher and is moving out of state. She put in her notice which would have her end date 2 days prior to the end of "clean up" (school will already be over). There was no issue at the time but now, and without explanation before hand, her current principal wrote her a scathing letter laying out in general terms, all manner of infractions and closed by saying she took it upon herself to call her new school to let them know the many ways she violated her contract and basically saying what a horrible teacher she is - she even said my DIL had "inappropriate physical contact" with a student. This comes well AFTER the principal had already sent a glowing reference! By the way, my DIL has not ever had any warnings, write ups or other negative actions. She received a call from her new school now and is worried she will be fired even before she starts. Seems to me this is defamation, slander and libel. Would appreciate your comments!