Why does Mrs. Johnson visit the Youngers in A Raisin in the Sun?

Part of the reason behind Mrs. Johnson's visit to the Youngers is out of plain nosiness and a sense of intrusion.  She is jealous of the aspirations of the Younger family and displays a certain sense of resentment towards them.  She raises the fears of the Youngers in telling them about the hate crimes that have been committed in Clybourne Park, the neighborhood to which the Youngers are moving.  Her presence in the play is meant to display another set of obstacles that the Youngers face.  Indeed, they are beset by the challenges of race and class.  Through Mrs. Johnson, they are also challenged by some of the members of their community, who privately covet the opportunity for success that is presented to the Youngers.