IMO, you're wasting your time trying to find WT info to support your contention.
You're right, of course, your daughter should be obeying you the same as if you were living in the same home and still married to her mother. Eph. 6:1 doesn't add "but not if there are legal issues."
If her mother is telling her that she doesn't have to obey that's not something you can resolve by "reproof" from the Bible or the WT literature, it's an attitude problem and she's choosing to act contrary to WT teachings. There's nothing you can do about that no matter how much evidence you have that she's going against the laws of her God(s).
The real solution lies with the courts. While they don't care what a particular religion teaches they do sometimes take action if the custodial parent is denying the rights of the non-custodial parent. Leave religion out of it. Make a list of solid examples where your rights were obstructed then take it to your attorney or to the family court. Make sure you leave emotion out of it along with religious beliefs; they're not going to enforce "Bible principles."
There is another angle to this situation and that is juvenile court. Regardless of the family situation a child who refuses to obey a parent while in that parent's care and custody (as in visitation) may be deemed incorrigible. Don't let your fear of losing contact with your daughter overrule your parental rights; let your child learn that her future is in her own hands, that it's against her own best interests to let her mother try to control the whole show.
Please note that in some places a 13-year old has the right to make decisions regarding acceptance of custody and visitation. If you live in one of these areas and she does not want to see or obey you she may have that right. Again IMO, if that's the case then let her reap the consequences of her own actions.
Don't destroy your peace of mind. You seem willing to do the right thing but if you're not getting cooperation then shake the dust off your feet and let peace be, at least, with you.
Best wishes,
AB