She is a weak character, with no clear opinion of her own. She is forever vacillating between taking sides with her husband and her sister - whoever happens to be more convincing at the moment. She takes the easy way out in a situation that she alone has the power to put a stop to. And because of her lack of decision things get completely out of hand and reach the point of no return. She eventually betrays her sister, lets her husband get away with rape, and in the process ends up living a lie.
Let's take the main players: Stanley Kowalski and Blanche Dubois are both strong characters, but they are the antitheses of each other. Blanche finds it difficult to face reality. She prefers to hide behind illusions and pretenses. As she tells Mitch (Scene 9) "I don't want realism. I want magic!" Whereas Stanley is as real as the piece of raw meat he handles at the beginning of the play. Blanche relies on the "kindness of strangers" (Scene 11), while Stanley is clearly a self-made man with his destiny firmly within his control - or at least till Blanche turns up to disturb the balance. He is honest to the point of brutality, unlike Blanche for whom 'life is too full of evasions and ambiguities', so she not only deceives others, but herself too.
Blanche describes Stanley as a "survivor of the Stone Age". While this is too extreme, Stanley is clearly a male chauvinist and has a rather primitive streak when it comes to women. He treats Stella quite roughly and demonstrates his power over women with his demands and aggressiveness, whereas Blanche swoons and uses weaknesses to get her own way. However they behave, throughout the play, it will be noticed that Stanley and Blanche are true to their selves, but the same cannot be said of Stella.
Stella comes from the same genteel background as Blanche, but she has chosen a more earthy and coarse lifestyle. Unlike Blanche who despite her checkered lifestyle is more of a romantic, Stella follows her basic animal instincts more than any intellectual or romantic call. Before Blanche comes on the scene, she is happy enough with her husband.
To his credit, Stanley welcomes Blanche with an open mind. He puts up with her fancy ideas about the dcor, the way she hogs the tub with her predilection for hot water baths, drinks up all his liquor (without contributing in the least towards the house) and flirts with his poker pals. It is only when she starts putting him down, and turning his wife against him that he feels threatened and strikes out - in an instinctive animalistic way, and then he goes straight for the jugular.
Stella should have been more sensitive to the needs of her husband, who clearly loves and cares for her. She has made a commitment to love, honor and obey him, therefore he should have been her priority, but she not only invites Blanche to stay, she encourages Blanche's disparaging comments about her husband.
Stella should also have realized that any houseguest is bound to upset the natural rhythm of a household. But with a dangerously disturbed and destructive guest like Blanche there's no way there can be any peace in the house. Especially when her husband and sister practically strike sparks off each other every time they interact. Stella should have made her choice a long time back, and ended