That's not being a good friend; a good friend would either not have pressured her into going, or would have accepted that the pressured agreement meant that they were going as a pair, and that part of Nancy's responsibility for the night was to ensure that Barb had a good time.
She talked Barb into going -- pressured her into going, more like -- and then didn't take care of her when she was there.
Allen Miles and Karen Lea have named their daughter, born Jan.
She teams up with her future boyfriend Jonathan Byers to investigate Will and Barbara's disappearance, which leads to her discovery of the Upside Down.