I think you are in a tricky situation since you work with her in a family business. The problem is if you and your daughter depends on the business then closing it will affect your financial situation as well. I think she is taking advantage that you rely on a business that was passed to her and she expects you to do whatever she wants because you don't have independence. One question is in case of a divorce what happens with the business? How do you take care of yourself? Do you share 50%?
I think she knows you fear divorce so much and using that to threaten you so you will be quiet. I think divorce hurts you but what she is doing is equally painful and destroys you. She can't be with you and the OM so it's best for her to make up her mind.
I don't think detaching will let her leave you if she loves you. I feel already she can do worse so detachment will just help you work on yourself. I feel she is being selfish & your fear of loosing her is what she is using to make you comply. Get over that fear because already you lost her. To get her back you have to talk to her but don't beg or make decisions for her. Work on any weaknesses you have and tell her you don't control what she chooses to do. Just tell her you want to work out things BUT she must respect you and work with you. If she wants a divorce that's her decision BUT you can't accept what she is doing.
M 11 Dated for 4 years before then Me 35 H 39 D 10 BD Feb 2016 A 2015 Dec I was never in a R with the OM. Had a one night stand & I stopped contact immediately I confessed the A to H and we went for MC