A mother's love is strong. You have to make sure that you keep your communication with her (which you have) Addictions are hard to break and sometimes the afflicted individual never changes. It seems that your husband from what you've shared may have a difficulty in grasping this. On a certain level (even if it subconscious), he may think that the way she behaves reflects on his ability as a father. In fact, each individual has the free will to behave as they are capable of.
You know both your daughter and your husband well. You have witnessed that no matter what you tell either one of them, they will still do whatever they want. In this case. you focus on what you can do as an individual and still remain able to interact with both of them. Even if one individual does not understand or approve of what another one is doing, it is not necessary to have ill feelings, stress or conflict. Your role would be that of a mediator. This can be possible when you neutrally acknowledge their behaviors and without judgment you continue to interact with both of them and to love them unconditionally. You and her father can only encourage a certain level of behavior in her. She is an adult and had chosen the lifestyle that makes most since to her now (either correct or harmful)