It's hardly likely that she'll make any changes to her relationship with her H ever, and if you won't be in the same room as him, then it seems to be her choice to go with him.
She's right about it being none of your business what happens between them privately, but you were actually involved because you had to listen to it, and were seriously inconvenienced. Your friend could have told her husband that you'd come a long way, and her arrangements had to go ahead.
I had a permanent break with a good friend, who we always invited to spend major holidays with us because her son and DIL would make plans that didn't include her. After we'd quarrelled, her son had to step up or she would have spent Christmas etc on her own. Point being that without you there her slob husband might actually be forced to look after your friend properly.
It's sad for you though, and I sympathise, knowing what it's like to distance yourself from a good friend. You might be able to keep up contact with phone calls to check on her welfare, but don't let them mess you around either.