Pot, alcohol or drugs are an excuse. Deep down inside they want freedom. Maybe they want freedom from the responsibilities of parenting. I hope she did not deliberately do this and use the “I’m a victim” excuse.
Regular people become addicts...and then do things they would never do when sober.
I know folks who became addicts just because of back pain.
Pills and eventually heroin.
This is a real problem of modern life. We can fix this but we have to address it rationally. Knee jerk reactions will not work.