Namsnannyto an outsider reading your post, it appears that something has happened and it seems that you don't know what that might be. However, you have been consulting your other ACs and the aunts and uncles so you have been doing a bit of talking to others that might have got back to your daughter and worsened the situation.
If you can honestly say that you have not been unpleasant then a few things are possible - your daughter might sincerely be horribly busy, they are these days, and parents demanding attention add to the stress. Something might have happened that she can't talk to you about - a marital crisis, a health concern, etc. Could she have been unhappy or depressed and /or been having counselling which has brought up things from the past which she is angry about? Could it be just that, in a busy life, your ACs get more out of each other's company and support each other to the exclusion of us? A little hard to accept but they are adults living very different lives after all.
I don't mean to be unsympathetic but you sound distressed and thus somewhat blaming and defensive. You need to find a way of calming yourself and taking a step back because the way you have expressed the situation is full of an emotional tangle that would make most ACs run a mile. Can you speak to your GP, a counsellor who will help you consider alternatives and perhaps find a way to contact your daughter and ask for a calm discussion of how you feel things have changed.
Some time ago now, we had a problem with our oldest daughter. She had been depressed and having counselling and was upset about things from the past that were a surprise to us. It took at least a year to sort out and we had to learn that her perceptions and feelings were hers and we must accept them without arguing. It wasn't easy but the poem by the Prophet with the lines 'your children are not your children, they are the sons and daughters of life's longing for itself......' became very pertinent.
I know how hurt you must feel, this situation may be a panic on your part and may be nothing more than ACs growing and life changing, but do see if you can find someone impartial to listen and help you. Wishing you all the best. 