ANDY'S ANSWER: The trick is to stay calm and rational and not fall into the "victim" role. When she's ranting on you for something you didn't do, look her straight in the eye and calmly say, "This is a stretch even for you. You'll have to find someone else to blame because I'm not going to be your excuse every time something goes wrong for you." Be mature yourself and don't get sucked into her drama, because as soon as you do, you lose.
I'm going to let you in on a secret. When you and your sister are adults, you will be each other's best friend. I know you don't believe that now, but wait.
Below is the recording of Andy answering this question.