Bipolar Having a Baby?

My sister is 34 years old, and having her first(and hopefully only) baby in about a month. She was diagnosed as being bipoalr about 13 years ago, and has experienced about 5 or 6 major manic episodes in that time. She is convinced that drugs trigger her mania, and if she does not use drugs, she will not become manic. She also thinks that having a child will make her stop doing drugs. I have had a strained relationship with my sister for my entire life(I am 28). Even as a child, I can remember her treating me very badly, and it seems that after she became ill, it got much worse. I feel as if she resents me for the fact that she is sick and I am not. I have not seen her pregnancy and impending motherhood as a good thing. She became pregnant less than a year after her last manic episode, for which she refused treatment and had to be involuntarily committed, just like every other time. In this last episode, she broke my mother's windshield with a mag light and accused my father of sexual abuse, which never happened. She has not told her obgyn that she is bipolar because she is ashamed and in denial. She is the most selfsih person I know, and I am terrified for the well being of her child. The father of her baby supposedly agreed to having a child with her, which just astounds me, seeing as he witnessed firsthand what her manic episodes are like. She has never taken medication, except when she has been forcibly hospitalized, she does not have a license or a car because she has had 4 or 5 DUIs(and still will not admit how horrible drinking and driving is). Her last DUI actually wrecked someone else's car on the highway. She chose to get pregnant while my father was in the hospital battling ALS(a battle which he lost in July), and has since quit her job and is relying on my mother to support her financially. This fact does not seem to bother my sister, and my mom will not talk to me about how she really feels. However, she must realize that if my sister has a manic episode, she will be left to care for the child, as I doubt the baby's father would be willing or able to do it. I am very scared about the postpartum period especially, and the effect that lack of sleep can have on a bipolar person. She is very unaware of herself, and totally in denial, so if she starts to have symptoms,I do not think she will reach out to anyone for help, and by the time we see them, she could be to far gone to accept it. I know that postpartum psychosis is quite common in bipolar women, and I am so scared of the what ifs. My mother is acting like everything is just peachy, which makes me feel like I am the crazy one for being so concerned. Please don't assume that I don't think bipolar peopel can be good parents. I am just fearful for my sister because she has never accepted her illness or done anything about it, in over 13 years. Should I just relax and try not to worry about things I have no control over? I am sort of preparing myself for a time when I may have to care for her child, seeing as I am young and have two children of my own, I may be a more suitable candidate than my mother to do so.