I’m so, so sorry for your losses. It’s natural to feel like you didn’t do enough and blame yourself, but it’s really not your fault; you couldn’t control your sister’s actions or choices. I know that doesn’t take the pain away, though. I don’t know too much about bipolar except that it looks difficult to live with as a mental health condition, even when treated sometimes (I don’t mean any offence to anyone who has bipolar; I’m just an outsider looking in who happens to have had two relatives with it).
I do know it likely contributed to my biological mother dying, about 9 years ago. The verdict was she didn’t mean to take her own life, but they couldn’t actually say 100% either way, and it was tragic, regardless.