You can block the emails and you can block her phone number. You just have to handle it through the carrier or provider. Your children's school should not be taking her calls and should not be providing her with any information. I would contact the principal and, if necessary, the superintendent. Here is a link for victims of stalking: ; http://www.ojp.usdoj.gov/ovc/pubs/helpseries/HelpBrochure_Stalking.html
This may be helpful. You may need to speak to a criminal attorney.
This answer is offered as a public service for general information only and may not be relied upon as legal advice.