The quickest and easiest method under Louisiana law, though also the easiest to undo, is to have your mother sign a temporary guardianship of your sister over to you. Mind you, this may not be valid or enforceable under California or Oregon law.
A temporary guardianship can simply be a written statement signed by your mother stating that she is granting you temporary custody of your sister. Though a temporary guardianship is revocable at will, so if your mother changed her mind then any rights to guardianship that you would hold would be immediately revoked.
The other issue to contend with is that you would need to get your sister back to Louisiana after getting that temporary guardianship signed over to you. Once she is in the jurisdiction of a Louisiana Court, and you have reason to believe that an imminent harm to your sister exists, you can petition the court for emergency custody based on that reasonable fear. The court would then set a hearing date to determine whether or not a permanent custody arrangement needs to be made.
If you have any questions regarding this issue, please feel free to contact my office at 337-237-0492 so that we can discuss how to resolve your concerns.
Answered on Jun 24th, 2020 at 1:47 PM