My seven year old TB (never raced but had a year and then some not working) acts the same way, I am ground walking her on my trails in the back yard… she is herdbound to one of my minis and I keep her focused on me… sometimes a tough proposition with 1100 lbs of TB spooking and worrying about her buddy but we keep pushing through it. I also do not have a buddy to go out with.
I make her do transitions in hand, slow walk, faster walk, back to slow walk, whoa, walk, try a trot if she is focusing on me for a few steps. The weather has been too crappy for riding but not for ground work.
She was balky when I first got her and it turns out she had ulcers - she would just stop and mouth the bit and once she looked at her side. She would try to start up but would then become nappy. Once she started the ulcer meds she was more willing but when she would act up I kept her moving and if she was quiet I would stop her. A work in progress but I knew I was getting a green TB. I hand walk with a stud chain… she is used to it and it keeps her mannerly. A rope halter also works for her. Good luck to the OP with her horse.