How do I deal with my anger?

My wife and I were asked by her Grandmother about 15 years ago to move in with her and help her take care of the big house that she and her late husband owned. When we got here, the house was a dilapidated mess. Full of trash and collections of bags, paper, cardboard boxes etc etc etc. We worked hard to clean it up and get some remodeling done to the house. It is a continuous battle to keep her grandmother from collecting more and more trash. I have to rip every bag to render it unusable. Soda bottles too. She lies to cover up her taking of trash out of the can to "reuse". I caught her today pulling a couple soda cups from a local fast food place that my wife and had been 3-4 days ago. She was using them as a vase for some flowers she had cut from the yard. I pulled the flowers out and placed them on the counter telling her "you have dozens of REAL vases, stop digging in the trash!" She said she didn't dig them out but I very well remember tossing those away a few days ago. (they were from Arby's, she doesn't eat at Arby's). She lied and said they were from when she and a friend went to Arbys. I called her on it and called her an out and out liar. A yelling match insued and my wife (her grand daughter) would not back me up. I was infuriated! I made my wife so angry that she hit me repeatedly with a coathanger (still marks). I'm going out of my mind living with this woman but we financially have no other choice but to stay here. So I need to make the best of a very bad situation. I need to know what to do about the anger that builds up in me almost instantly when she lies and digs in the trash. (p.s. I know it sounds gross but I've had to resort to pissing on the trash outside to make it smell so she won't dig it hasn't had ANY effect )