Calling it Co-parenting is kind of a joke.
When there is out-and-out hostility between the parents, or when one parent just isn't capable of acting right most of the time, "co-parenting" probably isn't a realistic option.
I've been divorced for several years, and my kids - now 16 and 17 - are doing very well. I still wouldn't claim to be "co-parenting", and that's not really my goal.
"Co-parenting" requires quite a bit of communication and coordination between the parents. If that's possible, great, but I'm convinced if I was to communicate that much with my ex, it would be a disaster. The only thing that has made my life work is distance from her - physical and emotional. I communicate with her by e-mail, but not very often, and only about practical matters - no emotions and no talk about the past.
Unless both parents are ready to act right, "parallel parenting" is a much better model. You take care of the kids when they are with you, and she takes care of them when they are with her. Minimize communication with the disordered adult. If you have reason to believe the kids are in danger, you have to step up and look for solutions, but if the risk to them is emotional, you can deal with that during the time you are with them, and with counseling from a professional.