Meth, adoption, family help, etc?

So, my sister is pregnant. I am too. She’s due just 5 weeks after I am so we’ve been pregnant together and everything was great until this past weekend. I found out she has to spend time in jail because she tested positive for meth on a drug test! Now I know she used to be on meth, and I thought she had stopped even before she got pregnant. Maybe I’m just gullable? I don’t know. But anyway, I’m not sure if she has to go to court ordered rehab or not. But even if that’s the case, if getting pregnant after 8 years of trying and knowing she’s got life inside of her, that she has to take care of doesn’t want to make her stop using meth.. I’m guessing that once she gets out of rehab she’s going to want to get back on it. And so I’m pretty sure she won’t get custody of her child, like.. as soon she’s born she’ll lose custody. Well, pretty much the rest of my family is on drugs too.. my mom, my dad, and pretty much every cousin I have. I can’t let my neice go into foster care! Even though I’d have a newborn myself, if I had to, I’d try to get custody of her. My best friend stepped up (who is also close to my sister) and said she’d love to try to get custody of the baby. She realizes what all could be wrong with the baby, but still *really* wants to give that baby a shot at a normal life. So I was wondering, what should she be doing right now to ensure that if my sister doesn’t get to keep her baby, that she could get custody of her? So she doesn’t fall into foster care. I have no idea how this works, and if my friend could even get custody of her. If she can’t, I definitely will if no one else steps up.
I’m all for my sister cleaning up and actually keeping her child. I doubt she’d give up rights as she does see herself as a fit mother. The baby’s father is involved, but is also on drugs. I understand it would be just foster care, the friend or myself, until my sister straightens up.
I agree. I can’t believe she is doing this. There are SO many things that could be wrong with the baby. The baby could DIE. She could be mentally retarded, etc. etc. etc. I seriously want to kill my sister, but that’ll help nobody 🙁