I hope you have documented this event in your journal seeing as it clearly demonstrates her inability to care for your toddler. Perhaps in the future, as you slowly prepare for divorce, it would be wise to take pictures of her passed out (with time and date stamps).
It's sad to have to come to this, but what jumped out at me is that she was alone, intoxicated, while caring for a 2 year old. Thankfully, nothing happened, but it could have and that is worrisome.
*hugs* to you. When you're ready to file, you'll know.