wow, Katie, this is such a sad situation for all of you. Unfortunately, you can't make her do something she isn't motivated to do yet. It appears you have let her know that you support her leaving the relationship, so that is about all you can do.
Maybe gently guide her, if she comes to you with information, or shares her pain and sorrow. If she doesn't understand the concept of codependency, perhaps you can explain that to her. Codependent no more, by melody beatty has so much affirmation in it for those of us who are wrapped up in someone elses addiction, or for those who need to work on their own self respect, in order to have a good life.
I hope your son finds recovery. I am so sorry for this sorrow in your life.
hugs,
chicory