Horse lacking balance, off in back end?

Question
I have a 6 year old Friesian Sport Horse (75% Friesian 25% Thoroughbred) mare. She is being ridden for a hear and half now, and generally doing quite well. Lately for the past month or so I feel her "off" in her trot (to the RIGHT - POSTING only) she is fine at the walk and canter both directions - now. Although up to a month or so ago she had issues with left lead canter, she just wouldnt take it or would counter canter. For about that time or slightly longer she is in training with nationally recognised andalusian trainer near chicago. Its barely noticeable when looking at her movement, but I can definetely feel it. My trainer gives lessons on her, and thats how he trains her most time, pushes her through the use of his students who may not be versed in how she moves, may not feel it or may not care that she is off... My trainer said it could be her stifle as lots of friesian have stifle issues. Please advise...

Answer
Hi Justine ... I apologize for the delay in getting back to you.  I was out  of town for the Labor Day weekend and literally just got home. Your question is troubling to me and I'm sure you can't be very happy either.  Red flags came out for me when you mentioned that this trainer is using your horse as a lesson horse and appears to be allowing students to put miles on her for them.  Was this the agreement when you dropped the horse off?  At just 18 months under saddle, your mare is very impressionable and is no doubt looking for consistency and leadership ... really hard to get this from a variety of student riders who are working out their own issues a her expense.  Just with the information you have provided, I would find another trainer and consult a veterinarian or equine chiropractor to have them evaluate why she might be off.

I'd love to hear what you find out!

Thank you Justine :)
Judi