As for our part? My husband and I have sufficiently communicated our concern/regard. What else can we "do"?
Be kind, be compassionate, but mostly be patient with your cousin. She'll have to come around on her terms on how to manage her life, and it may not be what you and your husband would like her to do.
And that can be frustrating. But it is what it is, and you have to remember that you're not paying a price. Your cousin is.