Goldwing, you have the right to be outraged by her mother's behaviour in bailing her out and then dropping her off for you to handle. Speaking from my own experience with my sister, her own family will be terrified of you divorcing, because that will put it all back on them.
It may seem harsh, but separating yourself from this madness and allowing your wife the dignity of making her own decisions, good or bad, will give you the best chance of building a normal life.