The character of Maggie is not focused on as much in the short story "Everyday Use" as Dee or the narrator. This makes sense if you analysis things properly because the character of Maggie stays in the background as well, so why wouldn't Alice Walker have her in the background of the story.
The crisis with Maggie would have to refer to the fire that burned her so badly. After explaining Maggie's character as being like "a lame animal", the narrator remembers the fire. She recalls this as a pivotal moment saying "Sometimes I can still hear the flames and feel Maggie's arms sticking to me, her hair smoking and her dress falling off her in little black papery flakes. Her eyes seemed stretched open, blazed open by the flames reflected in them." Meanwhile Dee was standing under a tree outside. It is implied that Dee started the fire that so badly scarred her sister and changed her sister forever.