Background for me - My grandfather lost his eye and arm in WWII. He came home help raise 10 kids (5 born after his return), worked for customs even thought Canadian Armed services considered him 100% disabled, built a little league baseball field in his back yard and hosted games for years, built a hockey rink in his back yard every winter, was active in his community. I know how my family would have reacted to someone like this.
Dave should have immediately informed Louise that due to her treatment of his sister no-one absolutely no-one from his side of the aisle would be attending. He hoped that her family and friends would have a good time.
Barring that only Dave should attend from his side - everyone who knows Susan should boycott the wedding. There is nothing wrong or rude with Susan telling everyone the truth.
Rude would be getting an advocacy group to protest the wedding. It would be a good day dream, though.