Absolutely get out!!!! Personally, I have enough troubles of my own without listening to other peoples nonsense - and that's what whining is - nonsense.
Our own quality time is limited, so why waste it with people who like to complain? I chose to be happy whenever possible and friends help make you happy.
I would go to the hostess after the meeting and tell her that you won't be coming for a while, for peronsal reasons, but that you'd like to keep in touch with her - that you enjoy your relationship with her, and that you will miss her.
If she presses it, you can tell her that the negativity is starting to get to you. Don't change your mind. Your mental health is so much more important than belonging to this group.
Not all older women are complainers and whiners. You and your one friend will have a wonderful time learning from and teaching each other.