Thank you for your question.
A 14 year old is still legally a minor, so they do not get to decide what is in their best interest - the court will leave that to the parent/legal guardian.
Do you know if the grandparents ever got legal guardianship
of the 14 year old, or whether this was just an informal arrangement between the mother and the grandparents? If there was no guardianship order in place, the mother is within her rights to seek return of the child to her. If there is a guardianship order in place giving legal custody and control of the child to the grandparents, then they do not have to return the child to the mother unless and until a court say otherwise.
If there is no guardianship order in place, the grandparents may still want to talk to a family law
attorney in their area to see if that is something that is worth pursuing. Ultimately, it would be up to a judge to decide what is in the best interest of the child
-whether it is to stay with the grandparents or not. The fact that they have raised her for her entire life does help, especially if the mother is a danger or threat to the child's safety or welfare in any way.
In a court hearing, a judge might
consider the wishes of a 14 year old, but even then, what the child wants is not binding - the court could still find the child should be returned to her mother.