Like a horse.....go back to the beginning.
Never use the word 'come' unless you can enforce it. Only use it or whatever word you want (may want to make up a new one) when you can tell she will do it...
Practice, practice, practice alot with treats.
Takes two people, one on either end of the yard. Start with a long leash to enforce it, graduate to her just dragging a leash. Never get mad at her, just distract and try again.
One holds her and the other calls to her to come, very excited, with treat when she comes and sits. Do this in the house, in the yard, everywhere you go....
Horses don't need the repetition....dogs do!
It is gonna be harder with an 8 year old, no doubt!
My dogs also know when I am really serious, I do the throat growl. When Angelina was young and seh ignored I snuck up on her and grabbed her so now she knows if she ignores I will 'hunt her down'. Doesn't take much with a golden retriever.
Cannella the younger is a different story and she is not let loose in 'unsafe' places period. She is too quick for me and her previous owners chased her so she knows she can get away.
I also cheat with a ball in my pocket or a small squeaky toy for emergencies...
I can only hope my repetition of training will sink in and if I really need it one day she will listen. (Like the other day when she got out of the front door and started chasing the jogger down the street....not good...at all and I wasn't home).
Some days I think horses are easier then dogs!
I hope this helps!