Sister in law trouble please help?

my sister in law was very good at first....she had earned place in everybodys good book.....now she is using this against me....i am usually outspoken.....this nature of mine is an added advantage for her.....she is now triggering me without any cause to fight with her......the most horrible thing is that even my mother is siding with her.......my brother has become more silent these days...and it is clear she is running things at their house.......i want her to stop this nasty approach...she is doing all this for me to initiate partition....i am married....my husbands family is on my side.....but now i don't have a voice in my own house becoz she has all the ground support.....i just want my mother to realize her true intensions.....please help