Stained Glass Heart, I feel your pain.
Here's my suggestion - don't have any contact with her - do not reply to emails, phone calls, nothing at all. I would not contact the police, if they should come to you, they will have to have some evidence. I have seen people like this talk about going to the police, but they are not credible and the police will recognize this in a heartbeat and start keeping an eye on THEM.
I would however get a new telephone number (a prepaid phone costs $20 a month and get a new email address - I would move all the contacts (whose who won't have anything to do with your son and his family) and isolate the previous phone number and email address so that they are the only people who might use them to try to reach you. This way when the phone rings you know it isn't them, and when an email comes in, you won't see their names on the screen. This shouldn't cost much money and you can point out to the police if they should ever arrive that you wished to protect your privacy from someone who wasn't trustworthy. Document everything 6 ways to Sunday and have other people document it so you have witnesses in the case of "she said-she said".
As for the lies, I had to combat some vicious lies that my ex told my employer and everyone else when we divorced. The lies were so horrible that some of the people wouldn't repeat them to me. At the time I was terrified that others would judge me and believe him. A very wise woman told me "What fools believe is no concern of mine", and over the years, I have held my head up high and walked through the thicket of lies that a number of fools have thrown around. It can take some time, but the people who respect you are keeping their thoughts to themselves and won't let some nonsense bother them, and they will respect you even more for the dignity that you carry yourself in the face of a malicious set of circumstances.
As the old saying goes "A lie goes halfway around the world while the truth is still putting on it's pants".
The British say "Keep calm and carry on"........what about consider moving about 500 miles away, perhaps a new job in another city? with a raise thrown in for a bonus? If you are a reporter, you can start writing a book......fiction of course, perhaps a screenplay that you could sell to Hollywood for a million $$.