Advice please.

I have replied that yes I estranged and no I am not amd never have been a drug addict and neither are my children. I haven't gone into any more detail. Even my brother chooses to believe her, although I did go back to university late in life to become a teacher so perhaps he feels it a justified belief. Who knows I am tired of trying to understand thi thinking. I cannot rationalise irrational behaviour.

It is all unessesary drama isn't it

Put the record straight and then move on. You don't need this negativity in your life.

I don't do drugs and neither do my children, they may have tried things and not told me, I wouldnt demonise them for it and have seen no evidence. My mother threw me out after my drink was spiked and I was attacked. I think that is where this notion came from. My job is very aware of her shenanigans because, obviously that sort of rumour would be devastating to a teacher. I have hair past my waist so can always do a hair strand drug test if needed to defend my honour.

I would tell her the facts of what happened, you might wish to make it clear you are not looking for contact.

Re the cousin I would reply:

Im not going to tell you what to think, I'll just ask you to consider this question:
If you had any proof at all of someone doing those things, would you
A: alert the relevant authorities and support services?
B: chat about it on facebook instead?

All the best, I have nothing to prove

She is publishing online that you have broken the law. That is serious. I would consider police/legal advice to get het formally ordered to desist.

Usually I would say "let her! By slagging you off she is only showing her true colours" but these are serious accusations.

I think I would send an email to my cousin and gently put the record straight and then leave it there and put it behind you. You don't have to prove yourself to anyone.