Call CPS and let them know the situation and that you are willing to care for your niece. You never know what calls have already been made. Offer your sister some time to get her life together and offer to take care of your niece during that time. This situation, of course, has to work for you and your husband. I adopted my niece and she is the best thing that ever happened to me
. My sister wanted a healthy life for her child and gave up her rights. It was hard for her, but I am still impressed that she made that choice.