The main conflict of the play is when Mary discovers her husband is having an affair. I always tell my students to look at when we know the outcome of the central conflict or when we see a change in the protagonist to determine when the climax occurs.
Mary's view of marriage at the beginning of the play is romanticized and traditional. When she discovers her husband is having an affair, she's devastated and becomes disillusioned with marriage. She divorces him but hangs onto the hope for a reconciliation until she learns he's marrying his mistress, Crystal. Mary resigns herself to living without her husband until her daughter accidentally overhears Crystal talking to the man that she's having an affair with. Mary's daughter tells Mary, and this is when we learn that Mary has changed her view of marriage. (the climax) Mary learns to accept the harsh realities of marriage, allowing her to fight to get her husband back. She learns that if she wants to keep her husband, she must have a more realistic, more modern view of marriage. Mary will use whatever resources she must to compete with other women for her husband and to keep her husband. Her reference to her "Jungle Red" nail polish at the end of the play indicates Mary is ready to do just that.