I have lived at my property for 14yrs never had any problems with any neighbours until 5yrs ago when a 60+ lady moved in for the first 6months she was lovley with me since then she has been a nightmare with me and its got worse since I had my son 3yrs ago now she has started writing nasty letters about me and my son but there's never my 17yr old daughter mentioned in any of these what can I do please help.

Nasty letters wouldn't be slander. They might be libel if she let someone besides you read them. And what's a question about suing someone doing in the "Criminal Law" forum anyway? Defamation isn't a crime (assuming you are in the US).

Who is she writing these letters to and why?

Who is she writing the letters to?

How is this harming you and how much money has it cost you

She's writing them to neighbours around the area that I live in who are also my friends and have been for a long time. She also intimidates me and follows me and bangs and drills all through the night.

So I assume your friends don't believe the letters. Have you filed an harassment complaint with the police?