Is your goddaughter still addicted? I gather she’s had treatment.
The matter is my fourteen years daughter is addicted too, thus I know firsthand how difficult it's to persuade such teens to make a rational decision.
When I talked about the treatment she wouldn’t object at once, but then she disappeared for a week. As it turns out, she’s embarrassed about this. Wouldn’t have thought she could be ashamed of something. Searching for the way of this situation, I finally found the information about special rehabs for teens here https://addictionresource.com/drug-rehab/teen/ and want to try, she'll be more comfortable with peers, I guess. Maybe this info can be helpful for you too.
Good luck!