Hi OP.
I've been reading since the first thread.
I went out with someone who lied and had others believe the lies.
I won't lie (no pun intended), it caused major issues for me socially, but it wasn't the first time I'd had to distance myself from a massive group of people.
I was lucky to have a small handful of people who did some damage limitation for me, who knew the guy very well.
I also had a major kick off in the school yard, when the local gossip-cum-fantasist spread something grossly exaggerated about the guy I was separating from. It was very ugly and I broke down big-time, years and snot, the works. But I didn't lose it at the woman, I simply put forward my position and what damage she had caused with her lies (can't go into that, it became a police matter) and if I hadn't been so exhausted from all the moving about and sorting the refuge etc I probably wouldn't have burst into tears.
The police asked if I'd like them to pay her a visit and warn her to stop all contact, because she was also sending me vile messages for days, via SMS, what's app, facebook etc.
In your position I'd download one of the cease and desist templates, fill in the parts necessary, photo the letter and send it recorded delivery to her house (it's only two quid or so, your ex could bung you the change) and hold onto the receipt.
I would state to the what's app group that you've had enough now and don't want to hear more about it.
I'd tell the school there's a situation and that you just wanted to make them aware as it may spill into the playground at break time do could they please keep a friendly eye on your dd.
And if you see the husband, a quick and curt "please leave me out of whatever mess is going on between you and your wife, thank you".
Keep screenshots of anything which has been written down.
I wanted to say one other thing but I've forgotten what it was.
You're being brave and calm and that's commendable. I do think this woman sounds unhinged and ah I remember what I was going to say - I'd be concerned she might set up a fake fb account under your name, using the exact photos you use etc and message him from it. And then say that you're still at it. Just keep an eye for that.