Unfortunately you need to tell the police to come and get her or contact the Child Protective Services. This will not only protect you and your family but get their family the help they need.
Something else to consider, the bottom line is the same; however, you did not say why the Mother kicked her daughter out of her home at 2 am. Was she caught doing something the mother won't tolerate? Like sleeping in her home with somebody else, etc...So unless you have the complete story and not just the kids don't assume the woman is the one with the problem. You or anybody else that takes her in other than the legal system might just be the one's with the problem and now mom has found her solution. Obviously she cannot take more of it. Been there and definitely got the t-shirt.