Oh she i bad news for sure. Does she live close to you? It sounds like you rent the house right next door to her or something?
This woman has no shame, she is a desperado from the sounds of it. What makes her think your dh wants to see her girls and to flash the muffin is just unforgivable. Geez.
Your instincts are right, she's a total scuzzball. I'm not sure that anything that you could say to her would change her behavious, unfortunately she's one of those women that gets off on chasing another woman's man. In the event that your husband (or anyone elses husband) fell for her attentions, she would toy with them for a couple of weeks and then grow sick and tired of them and discard them like old trash. I gather that's what's happened with the boyfriend. Either that, or he got sick of her flirting with other men like a total trollop.
Don't you leave your husband, he hasn't done anything wrong, correct he may not be as forceful in getting rid of her as you would like, but it's not his fault she is acting like this. And that would be letting her win.
I'd seriously be looking at moving. And documenting all of this behaviour just in case. It's women like that that will shake their tail at anything that moves, and then when someone weakens they're out screaming rape.
This situation is only going to get worse as I see it.
Get out. Give her notice, find somewhere else, move on.
Done.