do not call your dil!!!!!!!
Do not 'engage'.
You will be entering 'her world' and putting yourself on her level.
You cannot have a rational positive effective conversation with somebody who is not rational or positive.
I am not writing off her 'cut you off' comments.
This shows signs of somebody who who is emotionally/psychologically troubled.
I actually do feel sorry for your dil (and therefore, your son as well)
you have done nothing to her...
She called you, and you have nothing to apologize for.
Why should you apologize for her actions???
Do not get drawn in....
simply screen your calls... And do not engage with her.
as another poster just said...
Your son is apparantly spineless when it comes to his wife.
If there is trouble in paradise (your son's marriage, new baby, etc...) then this is up to your son to deal with.
Tell your son that it is up to him to find peace in his marriage.
Tell him that you are very sorry, and you love and support him, but that you feel it is best to stay back and not interfere.

something tells me that if this young woman is so angry, demanding, threatening to 'cut people off' etc... That your son is also experiencing being on the receiving end of this.
Support your son, but do not personally engage with your dil. This advice stands for both of your sons.....
note: Very important here... I don't care what your daughter may have overheard.... She should be under orders to refrain from having one word to enter this fray... Now you are in the situation where this is affecting your younger daughter... You should refrain from 'engaging' with this dil (both of them) and your daughter should be under orders to do the same.
this situation should not involve your younger daughter, at all. If she becomes involved, it complicates matters, and gives your dil's an inroad to try to come between you and her.... If she texts them, they they are then free to text her back, telling her what a despicable person/mil/grandmother/and, yes, mother that you are. You do not want to go there.... Not appropriate... I would have a talk with your daughter, and advise her to step back, and to have no personal communication with dil.
And, op.... Just to be truthful here.... You are the one who voluntarily opened up and posted details of your family situation, your daughter, etc... And, yes, from the other side of the screen here, from the outside, it does sound like your daughter could be perceived as 'the golden child'. Just something for you to think about. Every single 'concern' that your dil covered were things that involved time and money that are spent on/with your daughter (while you do not do enough for them). That is just self-explanatory.