Disunited Canter Help

[Hey Hey]

Hello

I have a 8yr old Standardbred pacer. I don't know her history so don't know if she has raced. She will trot perfectly out hacking and in the arena and canter out hacking. However when i ask for the canter in an arena, she becomes disunited in the canter. How can i encourage her to canter correctly without being disunited?
Feet checked, dentist up soon and vet checked her over a few months back. She has always had a disunited canter in an arena whilst i have had her.

All help appreciated, thanks in advance.

 

[Kenzo]

Have you had her back checked, I know you said the vet has checked her but they don't always spot things, maybe explore that area for peace of mind, could just be that she needs more work (the right type of schooling to correct and develop her way of going, rather than anything being drastically wrong as in soundness issues.