I think my mother in law is too controlling of the family.
How can you say that?  What makes you feel that way?
Whenever I'm about to say something, she finds some reason to silence me
It's good to get things off your chest, and to raise issues honestly with family.  You should be persistent if you have something to say, and let your mother-in-law know that she shouldn't always cut you off.
We can't open our mouths in front of her because we fear that she will say we are wrong.
Best to be the one who speaks up first. It could empower others to do the same.