It's annoying and for your own personal well being you need to separate. She isnt coping with having a child with a disability , that's normal.
She probably is in financial difficulty but trying to keep up appearances by living on credit cards, again she can't have a disabled child as it doesn't fit with the overall perfect lifestyle.
The husband probably doesn't pay her attention coz if they been together long enough, the relationship may be stale, she's wearing thin on him due to her demands, or maybe he made a rod for his own back claiming to provide a lifestyle that he's probably tired of. Who knows?
Walk away or don't walk away. You're the one that has to or doesn't have to listen to it

Materialism for you.......can't blame her, it's a very dominant narrative

I make an effort to cut out toxic people from my life now. In fact, I make it a mission to free myself from the likes of these energy dampeners.