@John ******
Ok if not officially married then you really don’t have any options. Thai law states that her assets will pass to a family member regardless that she may have made a will naming you as an heir.
You can continue to stay in Thailand on your retirement extensions but where you can stay and those options will need to be checked with a lawyer who’s familiar with Thai estate laws.
I believe in theory that her estate would pass to her daughter, however I am not up on the legalities of this as she’s only 13 and there may be many more reasons that that can’t happen or consequences. You need the help of a professional.