I have a similar situation, with my cousin, who has bipolar disorder as well.
With her disorder, the times she was nice to me was amazing. She was great to talk to, and I made the mistake of getting close to her. The times she was suffering from her disease, she was unbearable. She used the closeness as a way to attack me. She pushed every button, tried her hardest to make me cry. She abused drugs and alcohol, stole things, broke the law. Her dogs suffered when she was in an episode. She was poison to my life, brought out the worst in me, and intentionally tried to alienate me from the family.
I let her win. I alienated myself. I don't talk to her anymore, I stay away from her immediate family. I got a new phone number, and did not give it out to her. The calls stopped, the criticism stopped. I am much happier and have much better self esteem without her dragging me down all the time.
A few weeks ago she tried to reach out to me, but clearly had not changed. She started pushing my buttons, trying to hit me in the sensitive spots, being critical of my life (of what she could see on my Facebook page, on which she wasn't 'friended'). I had to block her on Facebook.
Your situation might be very different from mine. Maybe it's different with immediate siblings. But for me, it seems, there are some people, even family, no matter how much you love them it is better for yourself to not have them in your life. You should not have to suffer, too, just because your sister is suffering from a disease. If you feel you are strong enough to handle it, that's great. But don't be surprised if things fall back into the same routine.
Stumbled into Primal due to food allergies, and subsequent elimination of non-primal foods.
Start Gluten-Free/Soy-Free: December 2012; start weight 158lbs, Ladies size 6
Start Primal: March 2013, start weight 150lbs, Ladies size 6
Current: 132lbs, Ladies size 2
26lbs lost since cutting the crap.