(((((lonelyperson)))))! give your sister some time. It sounds like both of you are still quite young, and often, people who haven't lived through a bit of pain in life don't have a clue when others have troubles. Such people will often distance themselves as far as they can from any they perceive as a "downer". she's blaming you probably because she resents feeling bad for you, but that is absolutely not your fault. If it's true, then she needs to grow up and stop blaming others for her feelings.
It's hurtful, but maybe backing off and leaving her alone will help both of you. It sounds like being with her and her attitude is really a downer for you. Don't hate yourself for other's reactions, we can't all be world class communicators. Do you do art? by the way?