Your daughter is married and her responsibility now is to her husband and child. If you want both her and your grandson in your life you must hold your tongue. You stand to lose them otherwise. You don't want to push them out of your life, do you?
As a mother of a recovering addict son, I hope his relationship with his current girlfriend is a healthy, happy one. I have thought to myself that his girlfriend could be in for rough times ahead, but so far they seem to be okay. If her parents were giving her a hard time over his past, it would make their relationship that much harder.
Be supportive of your daughter's life. There may come a day when she needs to talk to you, but as it now stands she can't talk to you because of how you would react.