I think if you can manage it, make a real push for victory over your own anger with this new counselling. I'm having counselling (for an unrelated issue to yours, but also through work) and I find it really helps to commit to the process, be honest and open and I now find I really enjoy my time with the counselor, who is lovely and not easily shocked - not that i have much shocking to say!
It's almost impossible to not think of something when the idea is in your head. Like the old don't think of a blue elephant! All you can see is a blue elephant. Can you switch it up a bit and think of a green elephant, and then a green tree, and so move yourself away from the anger towards her? The anger is only damaging you, not her, she seems to love it!
I think it is also really hard to just change your thinking. It may help to change other things too, take up a new hobby or sport, even something small like going for an hour long swim once a week.
The change in activity might help you to change your thoughts.
Lastly, I am furious on your behalf that either friends or family pass on news you do not want to hear!
"other people tell me what she's been up to whether I want to know or not."
Just get into the habit of saying clearly and plainly "Don't talk to me about XX I don't want to know."
If you are standing up just walk away as they are talking. Maybe a "Didn't you hear me?" Then rinse and repeat.
If you are sitting down then stand up, go to the loo, go to the bar, go and make a coffee, whatever you want (depending where you are).
If they really will not shut up I'd say. "The fact you want to tell me all about XX when I've said not to suggests you are a bit hard of hearing today, so I'll speak to you later when the wax is gone!"
You can cut out of your life anyone who doesn't want to listen to. Because ultimately their choice to tell you this stuff shows they do not respect you. Spell it out for them, I won't stand here and listen to news of XX.
"I think she is jealous but more than that, she's immature and loves the drama. I think she loved the fact she 'stole' my partner away from me and can't help trying to get mileage out of it."
The trouble is every time you get upset and talk about her to friends etc, which may or may not get back to her, moan about her (if you do) to your ex, which will almost certainly get back to her; you are feeding that bit of her that loves drama. You are reminding her how important she is (how clever she is) that she has done all this!
Of course she is not clever, or important, and I don't think it is all down to her. But your anger and hatred may well fuel her feelings of loving the drama.
"I know she's sad. I just don't understand people like that." No, me neither, I'd rather be kind than cruel. Maybe she has had a very shit time of it, and maybe she will have more of a shit time in future as there are no guarantee your ex won't do to her what he did to you.
If you can find it in your heart, just feel sorry for her; you got out, she is still stuck there with him.
Just make sure you protect the kids, protect yourself and make the very best of your new home, a new start, focus, focus, focus on you, the kids, and the future - not on anyone or anything else.
[hugs] 
XXX