I'm married to the love of my life who has two sisters. He is the oldest one. He always told me that his parents took really good care of him paid for his collage , MBA he had everything he wanted in life but at the same time he wasn't spoiled . His youngest sister who is 25 now is a big pain for me. Because she doesn't do anything in her life but waste her parents money, gives me attitude like she is the boss in the house( even though we pay for the house nd she lives with me and my husband ) leaves dirty things around the house and every time my husband makes a comment about something she did wrong she just turns in to a big drama. Now we don't talk at all anymore but my mil keeps calling my husband and telling him that his sister doesn't feel welcome in the house that he should apologize to her . She made me apologize to her because my sister in law is " depressed , she has no friends or boyfriend even though she is good looking" I said I was sorry that I complained that she wasn't tidy around the house and all I got back was " doesn't sound honest to me " . Long story short , I feel that my mil is not being fare here she justifies her daughters behavior regardless. She locked me outside the house to freeze because she is not too smart and locked the door wrongly , I save her dogs from being hit by a car - never said thank you, every time I cook I offer , every time she was sad I  took her out dancing whatever , I always bought her little presents to cheer her up . Now my mil wants my husband to apologize to her because apparently  she doesn't feel welcome here because we are house owners now and don't let her be dirty . 

I'm 26 , I work hard in my life for everything so does my husband . Why should I be more mature and keep being nice to her until she calms down and becomes a normal human being ? I'm only a year older . 

DOES MY MOTHER IN LAW HAVE A FAVORITE CHILD? 

Thank you all and sorry for the long post .