Mother and Daughter Help ?

Why does a mother treat you like you are a black sheep of the family all your life and she has two daughter's? She live's there with her four kids and husband and her sister with her 2 kids also live's there with the mother but she has always treated her youngest daughter like she is a blacksheep of the family, constantly calling her and her husband name's, cutting them down. Instead of encouraging her daughter, she tells her that she can't do it or calls her crazy or stupid or B**** or W**** or some name like that. But the fact is her daughter and husband buys $550.00 food- pays half of the rent and half of all the bill's and help's clean every night after supper but her other daughter only buys around $200.00 food and pays for nothing else, she has a free living with the mother and father. The mother has put her one daughter so badly depressed that she is thinking of committing succide. Nothing ever is good enough for this mother, no matter what she does for her mother, she still is the blacksheep of the family, she truely acts like she hates her. She tells her mother shes moving out with her husband and kids and she manulplates her to not get a house, this women really knows how to make her feel sorry for her. Everyday it is like this around that house, she's is calling her all kinds of terriable names and cutting down and making her feel like there is no hope for her life nor the future nor living. Does this women really hate her one daughter? she treats the other daughter like she is perfect, she provides everything for her, she gives her a free living and she acts like a real unconditional love to her. why does the women do this? she has told this women a million time's how she feel's about everything and all she saids is you are crazy, saids shut up b**** or your a wh***. so telling her how she feels does not work because that women just does not care.