Personally, I would just put this one down to incompatibility.
Of note, she avoided dinner with them all week....hurt her ankle and agreed to dinner...but after they went out of their way to treat her injury and buy painkillers...she found a reason to not go to dinner. Surely
you can see what happened?
She snowboarded on this 'injured ankle' the day after...again, surely
you can see the pattern in all of this?
I don't think it would have mattered how
you handled it - the result on her part would have played out in some way to excuse her from going to dinner.