I think a good way to deal with any comment like this is to put yourself in the other person's shoes. What if you were put in charge of taking care of someone else's kids for several weeks because of their alcohol issues? You mention you've gone to great lengths to ensure that it would be as non-disruptive as possible, but remember why they are there in the first place - because of your alcoholism. Your mother may also be feeling some resentment herself and blowing off steam with the comment.