Go is not using her "ring of muscles.' She is stiff... and her neck is up and her back is hollow. I almost she is missing some serious foundation work.. training her to stretch her top and engage her abdominal muscles to form a balanced, rounded frame. OR she could have a sore back.
Is she fixable? If it is training, yes. If it is a sore back.. maybe. It will take a lot of time.. lots of hills.. lots of work at transistions and balance.. getting ther to curl her rear under her, lower her head, relax her neck and work off her hind quarters.