I don't know how much help I can be, I have bipolar disorder but I mostly withdraw and try to hide my episodes from people. I had a few angry ones before I got put on medication but nothing like you've described.
Is your sister on medication? If she's just started it might take a while to find the right one or for it to start working. Medication might help a bit.
I don't think a lot of what you describe can be explained away with bipolar. Others might have more insight into this, but I think she might need some tough love. Bipolar sucks and you get angry or elated or upset or suicidal but if you just sit back, it's gonna keep happening. It sounds like she needs to take some responsibility for her disease. She might not realize this. It sounds like it's really hard to put up with her.
I couldn't tell you what to do in the situation. My position is that bipolar is something to be taken seriously, but not as an excuse for everything. It impairs my functioning, but I also know that if I'm proactive I can sometimes intervene and control myself and lessen the intensity of my episodes.
It must be hard to feel like it would be your fault if she did commit suicide. You can't be responsible for that kind of thing, it's not fair to you. You do what you can, and overextending yourself just hurts you and might make you less available. You are not responsible for everything.
To me it really sounds like she needs to take some responsibility. Sitting back and blaming bipolar is not going to help anything. Is she seeing a psychiatrist? Someone professional might be able to help your sister, and your family.
Hang in there.