Hi Lucky,
Your DH's ex seems a little like my DH's ex, except they have two boys (18/23).
She's so good at manipulation and convincing the boys how they have to take care of her, especially when she's being awful and abusive. She regularly pulls out these types of sick games, so we're not surprised anymore, and she's convinced them that everything's all DH's or someone else's fault, so she accepts no blame, thereby continuing her stronghold. And yeah, she knows how to work them over, and keep them away from DH, etc.
She's really good at the charm thing, has a lot of people fooled. It really gets to me that the boys have this sick relationship with her. She's trained them to be co-dependent with her. They don't see through it, they are stuck in the fog.
Yeah, one day she'll be abusive, and the next she knows what to do and say to keep them attached to her. But isn't this all N's?
They are so destructive and selfish.
Good luck,
KatG