I would be definitely recording that message on my phone and sending it to both of them.
I would then tell them that I am very hurt but am open to hearing what I have done to deserve such vitriol from her.
What your DIL did is not normal.
They both need to hear it.
I agree with the poster you quoted that she really doesn't like you and you need to find out why.
If she is normally quiet, it sounds like a pressure keg situation
You are the caused of such strife between them and your son is a mug?
That sounds like an ongoing issue that has finally boiled over.
Are you very demanding of him and his time?
Brushing such vitriol under the carpet will be too difficult, so best to get an idea where it comes from and can it be fixed.
Be prepared perhaps hear some hard things that may hurt, but at least you can try to rebuild the relationship.
I have no doubt it would have been very shocking to hear.
I would absolutely hate to be a bone of contention in my childrens marriage so whilst you have every reason to be very hurt, reflect on it honestly before you speak to them.
Wishing you well.