insurance. Public entities in Idaho have an insurance pool for liability insurance. The pool will settle most claims that are less than $50,000 because it costs more to litigate the claim.
My suggestion is that your wife document each incident and email reports of the incident to the principal. If your wife feels she is being harassed by the student and the principal won't do anything, then you need to get an attorney and provide them with the evidence the principal won't do anything. Then have your attorney contact the District's attorney. I guarantee it will get taken care of very quickly.