Yes, seriously. There's a good chance that the more negative you are about a relationship like this, and the situation, the more she will want him. In a way it's almost like dealing with a teenager.... the things mom and dad don't want them to do are the things they are drawn to most, and once it's okay the novelty usually eventually wears away.
Here's another way to look at it. You've already tried being against this whole thing, pointing out OM's faults, trying to control the situation, and use logic to bring her back, etc... and it HASN'T WORKED. So if it doesn't work, try something else.
Perhaps doing the opposite will be more helpful (and maybe not!). But at least it's different and there's always a chance it may work. You can only try and gauge results.
Keep up the good work on dropping that rope. It's painful, but you'll get there. Have a great weekend. Do something special for yourself.
There is no arriving, ever. It is all a continual becoming.