I'm surprised you didn't mention the annoying issue of becoming stupider on pot. There is a reason they call it dope. My H smokes it for arthritis and talking to him is just about impossible when he is high. I don't know what to tell you, if you do come up with a solution, please let me know. Big hug for you.
P.S. He does work and doesn't smoke when he is working, so maybe insisting she get a job.....any job....might help a bit.