Having issuse with my daugher!!!?

My 12 year old daughter Maddie is a big problem. She is rude is always talking back and is very mean to her 7 year old sister Sammy. She has 2 younger brothers (4 & 1 years old). I don't know what to do with her. She never listens and always has something to say. 3 years ago she was diagnoused with ADHD. She is in 7 th grade and hates school. She gets good grades but has issuse with girls at school. She is always made fun of but does have a few good friends. I am a single parent but Maddy has a good relasionship with her father ( she sees him every weeked) also maddy has a diffent dad then her siblings. Anyway, she is a nice happy girl but latley she is rude mean and less happy. How do i get her to.be less rude, nicer to her sister, and just behave!!!! P.S. Sorry if my spellings wrong I am using my iPod since my friend is borrowing my laptop.