If you put yourself in her shoes....would you rather know the truth so you have an opportunity to improve and thereby preserve this wonderful history with all these fab girlfriends....or be left in the dark and shunned and struggle with what happened??
If after 8 yrs. of getting together and she has not learned to take social clues from the group, like basic taking turns when telling a story and showing appropriate sympathy, then I doubt being subtle will have any long term effect.
I think it will be easier to hear this news from one person in the group as a spokes person and not all coming at her at once. She will feel attacked otherwise.
And finally, you all might have to accept that this is who she is by design and nature and if she doesn't get it, or doesn't want to get it, then she needs to find other friends to drain over the years.
Ultimately, she's the one who has to decide if she is going to be continually grumpy and unappreciative of heartfelt advice from her friends of 8 years. Or is she going to mature and give back and be there for you all as well.
My hunch is that her behavior will improve for a short time, but eventually revert to her old mind set. So you all will have to keep clueing her in, especially during times of stress.