Hire a private investigator, I am sure within a week you will get some answers and go from there.
Problem is, you are so naive and not private to the point you are letting her know about this thread. If you hire someone, then stop talking about it to her period so she does not know about the investigation idea, hence she wouldn't change her overall stances when you are not around her.
Bottom line, in your place I would not even give her some time to fix the damage she is causing in this relationship as you've written previously, and, even if she fixes it, the outcome would be unnatural and without any feelings/emotions, I do believe this is not what you are seeking.