Husband's sister interference

Our family consists of 4 ppl -me, my husband, my father in law n my 19mnth daughter, my mother in law expired 8 yrs ago .every time we have any dispute ,my husband calls his sister asks to interfere in our matter. i asked him y do u make her interfer in our matter so he says that it is her responsibility .he further says she has taken the responsibility of our marriage n so i agreed to marry ,so whatever happens i will tell her. now even after 4 years of our marriage she still present i m at my mom's home with my 19 mnth old daughter since 10-12 days as we had some dispute n he asked me to go to my mom's home.n yesterday my sister in law called my mom n told her that if i want to come back i.e., to my husband's home 1st i will have to give them in writing that i wont leave home again,etc,.on a stamp paper.n not to call my husband n call her whatever my decision would be.n if i dont give in writing i need not come back. my sister in law is married n lives in our city. so i basically want to know can she decide whether i can go back to my husband's home or not?can she interfer so much in our matters?to what extent she has rights in interfering in our home n our matters?