Pain causing horse not to pick up correct lead?

My girl has an interesting problem that I'm trying to get to the bottom of and would like to know if anyone else has experienced this, and if I have explored all my options.

Dilly has a hard time picking up her correct lead when we canter to the right. To the left she's perfect, very soft and balanced and she never picks up the wrong lead.

But as soon as we go to the right, different story. 9 times out of 10 she either picks up the wrong lead, or canters disunited.

At first we thought this was a training issue. But I've had my coach, plus another trainer at my barn ride her and they too have a hard time with her lead to the right, although they are much more successful at getting her lead than I am, it's still a bit of a fight with her.

Lately, she's so fussy when we ask that we're now convinced it's definitely another issue aside from the training. She either hollows out or pig roots through the transition, and once in the canter will either rush when asked to switch leads, or buck.

The saddle fitter is coming out next week, even though we had one out a few weeks ago and her saddle fitted fine at that point. It will be of interest to note that she does this saddled AND bareback. I'm also going to have the vet look at her and possibly a chiropractor.

I'm paranoid that this is going to be something serious. Obviously I will wait for the word of the pros, but has anybody heard of this or had any first hand experience with this?

Will she take the correct lead when she is loose or on a lunge line?

For the most part, she really favors her left lead; she will sometimes canter on the correct lead loose, in fact I've seen her do a fantastic flying change once while busting it up out in the pasture. On the lunge line she canters on the wrong lead or disunited.

You would seriously think she's a TB fresh off the track but she's a WB.

Also, I've had some canter issues with her in the past with rushing and leaning on my hands, so don't canter her too much anyways. Mainly stick to trot and walk, which she is totally fine in.

It could be an injury or it could be a balance issue.....

Sounds like a crazy problem. Let us know what comes out of the vet and chiropractors. I'm sure something is going to come up.