Big John, my nature would be to do exactly as you have suggested. However, you might want to get some advice from some others who have been in your shoes, like Stuck, Puppy, Coach and several. It appears to me that some kind of move on your part is needed, but that is just "me" and not necessarily DBing. I certainly agree with the financial protection of your accounts and credit cards. It doesn't seem right to me that she takes advantage of living under the same roof as you while continuing her PA. That causes you to support her while she has an A. If you could afford to talk to one of the DB coaches here, it would be good counseling. I don't want to steer you wrong. My biggest problem is not moving into action. But I like the ideal of you going to get your children and your car and leaving her to get back home the best way she can. I think that makes a very strong statement that you are protecting your children from her adulterous lifestyle and you do not intend to enable it. Personally I think it is time for daddy to step in and get his kids and take them home. I think that has a wallop of a message even if you don't see her or say one word to her. You would be the "Knight on the white horse" but it will be for your kids...not her!
I would think the first thing she needs to discover when she returns home is that she cannot suport herself (which she already knows, but you've been doing it for her). Time for tough love! She has already run into the arms of OM in spite of all you've warned her, so what do you have to lose? You've tried to protect her from OM by telling her what sort of man he is and she won't listen, so now she seems to need a reality shock. Besides, I am wondering if she is thinking you are going to take anything she dishes out just as long as she won't leave you. But she won't respect you BJ, and I believe it's important to have that. This is a critical time to make the right decisions.
It is not about what you feel should work in your M. It is about doing the work that gets the right results. Do what works!