Try and look at it from her side as well. You sound so angry and wronged, that is probably how she feels too.
She was wrong to go to the hospital, of course she was, and I don't condone that for a second. But I can see why she was angry, she was due the maintenence payment on that day, she didn't get it because her ex had something more important going on, but in her eyes his children should be the most important people in his life. It has to be hard to adjust to the fact that he has other priorities now.
How do you know her HV has referred her to parenting classes?
Have you reported her to her work about the fact you think she looked at your medical records? If so what do you hope to achieve by that? She could very well have heard from someone else about your PND and if you have been to her work before knowing the full facts that is going to have a negative impact on everyone including the children. If you have been to her work and it gets proved that she didn't look at your records it makes you look vindictive.
You keep on saying how the kids have more fun with you and what a shit mum she is, this attitude is something you need to stop. Kids pick up on things like looks, snarky comments and attitudes. It is so out of order calling her a shit Mum.
You say she palms the kids off on 'anyone' 3 nights a week. Really I doubt very much she goes out 3 nights a week, and the people who are 'anyone' to you are probably very good friends of hers.
You can't blame her for him being in debt, given that the house is on the market and in his name I assume he will be getting at least 50% of the proceeds from the house so its only right and fair that he pays 50% of the mortgage. This is a seperate issue from maintenence.
You say everything is about control and money. Well he does have to support his children and she has every right to maintenence. The control, I assume, is coming from her not wanting the children to see you. You have made a bit of a rod for your own back there by sending a message to her, you say it wasn't nasty, but then you say she threatened you with the police. Be honest, with yourself if not us, that there must have been a nasty element to it, you were obviously, and understandably upset after her showing up at the hospital. This could now be used by her to prove that you don't like her and therefore its not the best thing for you to be around her children.
I understand your feelings and its hard to see beyond your own viewpoint sometimes but you need to try and see whare she is coming from too, its the only way this can move forward.