Zappy, you wrote "Nobody in my family has ever had an alcohol or drug addiction so this is new terrority for me". I have found out the hard way that alcholics are really SPOILED BRATS. Once you have set down your house rules with your sister don't expect her to honor them. The only thing that alcholics care about is how are they going to get their next drink or fix. Even if your sister doesn't drink in your house, she will have "stinking thinking", and try to control her environment, your home. I think I understand why your sister's lawyer told her not to go to a sober house. He's not there to help her get better but to win her case for her. What I read in your post those two goals are in opposite directions. If your sister isn't supposed to be around her own children, why would you want her to be around your two year old? What you will end up with will be two two-year-olds having two year old temper tantrums.
Remember:
You didn't CAUSE it
You can't CURE it
You can't CONTROL it.