Heroin metabolizes into a morphine compound in the body, and apart from alcohol is considered one of the most difficult substance to quit.
She has a history of substance abuse in her family and is now addicted. If she is like most on this drug she will do nearly anything to obtain it. That means that trust is not typically something that is seen. Therefore, unless you see behaviors that show she is deadly serious about getting help, as the owner of this home you are in a serious position.
She is using this drug on your property. You know it, and probably others know it as well. Although it is tough love, she has given you little choice here. She needs to either show that she can get help, or leave. And, I would make this a short deadline of a few days (or less) and she must go. This is indeed caring for her, and no one can help her until she sees that need. As it is, the home provides an blockade to that process and in my professional opinion, as well as many who work with alcohol and other drug addictions, it is time to apply this method.
True, you will not be popular, but it is done out of love. Steven