Legal Question in Family Law in Texas

Are you sure that you have a guardianship? That is handled in probate court. It is totally different than conservatorship which is granted in family courts. They are totally different. A guardianship might not end when the child turns 18 - it goes on until the judge removes it. The "child" has no rights & is under a court's control for their entire life if necessary. So you might need to have an attorney review your paperwork.

You can certainly call your local policing agencies (police, sheriff or constable) and see what they will do. In Texas, a child is a minor until the moment they turn 18. However, sometimes the policing agencies won't want to get involved with 17 year olds.