17 year old moving out in Texas

my 17 year old sister is living with friends since my mom was evicted last month. she has been there 6 weeks, working part time. she pays no rent. She wants to move in with my family but are wondering what problems we may have if my mother fights it. mom recieves support from their dad for her and another child (my father is a truck driver and has no home since divorce last fall) and she will be concerned about losing the money. My mom and youngest sister share one room she rents from a guy out of his mobile home, my sister really does not have room there. She has recently been stressed to the point she has burn marks on arm from cigarettes, self inflicted. My mother has a history of emotional and mental abuse and neglect (they neither attend school or have benn homeschooled for more than a few days at a time in her life) and physical abuse with my brother and i. We don't want to have a court involved but are concerned about sister's well-being. Please help, any information would be great!

Why would your mother object to your sister living with you, but not to her living with friends?

Your sister is already out of her mother's home, and if otherwise self-sufficient is probably a good candidate for emancipation. Otherwise, you may wish to consider obtaining a guardianship.

my mom let her live with people two houses away. Control is very important to her. My sister had to quit her job this week and cannot get another. My mother "lost" her SS card so my sister found a copy of birth certificate and had a friend take her to apply for another. When my mom got the certificate back it too got "lost" and when the new SS card arrived by mail it went "missing" too.

My fear of trying to get a guardianship is my mother might try somehow to retaliate against us. What is neccesary to do this? my stepfather would have no problem with it.