Daughters don't get along

My 11 daughter and 18 daughter are both always fighting. They both hate each other because they are so different. My 18 daughter is like me and she likes girly stuff and pop music. My 11 daughter likes boy things and metal/rock music. She has mental illnesses and her sister says she is a "queen of sassiness". She is unlike anyone in the family. My 18 daughter would make fun of her and tell her that see is a kid and has nothing to worry about. My 11 daughter would talk back and she never opens up to her or me. She is always mad from school but she doesn't get bullied and she looks so sad every time to go there. Not like how you would when you have to go somewhere you hate but like when you have to suffer from something bad. I talked to her school but she is doing good in grades and is very quiet and does not get bullied by kids. My 18 daughter would go to work and always tell me what is wrong. She would also tell me about bad things about my daughter in front of her and would take videos of my 11 daughter without her knowing. She got caught and they were fighting to either upload the video to the internet or to delete it.Sorry for my English. I am still trying to learn it via /r/Parenting http://ift.tt/2uOG48v