Well, I don't want to dwell on this...but when she opens up a checking account with OM I think that's a pretty clear indication that the door is shut and deadbolted.
She sounds pretty flaky to me, it sure didn't take her long to shack up with someone else, and now a joint checking account? Wow. And yet she still has most of her crap at your house. Not exactly a model of stability and smart choices.