I would second Tom Beech. He identified exactly where my mare had a problem in her back, wrote a referral letter to the vet hospital telling them what the problem was which they confirmed through ultrasound and were able to medicate her.
I have had Tom before for BBP so I would definitely consider having him out again. I do have an excellent osteopath already, so will give her a go first (sadly until now I could not afford regular treatment, and I think had I used her sooner I would have seen greater improvements already)