Wear marks on left hind foot

I have an 8 year old Arabian mare, under saddle now for a year and a half. She has done 2 - 25 mile LD rides. I have noticed since training her that she has more wear on her left hind toe. She did initially have some wear on both, but now only on her left. Any thoughts on why this could be?

This is barefoot?

She carries herself asymmetrically.

Or:

Her trims are not balancing her hoof correctly.

Discuss this with your trimmer.

Mild asymmetry is within the realm of normal.

Can you post pictures?

Where is the wear? If it is toe is she.dragging that toe which could mean stifle or suspensory trouble?

Get some video of her moving towards, away, and past you on firm footing where you can see the hoof land and take off (not in deep sand arena). Play it slow motion and see if you can see any difference in how she uses the hind legs. Post it here if you want more eyes.

Or get an appointment with a good lameness vet.