@Brokenn
I can imagine that, because of all her shenanigans, this behaviour is foremost in your mind and causing you untold mental distress so I empathise, especially as you have your own DC now and will be in "protect" mode.
Can you not try to grey rock her?
She threatens to turn up at your house, I assume she hasn't already so probably won't?
Get a ring doorbell or cameras.
Social media post, ignore them, who cares, most people will read them and roll their eyes.
Text messages to DC, don't look at them, let DH deal with them.
DC wants to discuss his "D"M you find something else to do, let DH listen to it.
She signs you up for something, ignore, bin or delete.
Make it clear to your DH that you are no longer going to allow her behaviour to affect your life, he deals with it, he is not to tell you anything unless you are directly at risk.
The authorities don't or can't help you (I'd check with a solicitor first to make sure you're not just being fobbed off)
You need to protect yourself mentally as this is taking such a toll on you.
It'll be very hard but it may give you your power back and remove her power.
Assuming you love your DH, splitting up seems an extreme reaction and who's to say that would end it, she's got you in her sights and leaving might give her another reason to harrass you.
She's clearly vicious with too much time on her hands.
Plus if you leave your own DC will be in that environment without you.