I know first hand how using or drinking can affect parenting. I am an addict and a mother to an almost-two-year-old boy. A few of the ways I have put him in danger:
breastfeeding drunk and high
driving with him in the car high
One time I got high and he locked himself in the bathroom and turned the bathtub on. By the time my husband got home, it was overflowing, luckily he hadn't gotten in!
He left right out the unlocked front door and got about half a mile down the road. Thankfully the cops found him and brought him home. I was sleeping and didn't even know he was gone!
Those are just a few examples. Daily life was so chaotic while using and caring for him. I hope your wife gets the help she needs.