So it was time to do some recon. I found out that Rosa was briefly trained by a friend of mine. She let me know that the mare has been ridden and even galloped, but because she is small and has a short stride (and the tb economy was down when she was in training) they decided not to continue with her.
So the good news is that she has been ridden and also had “no buck”.
Meanwhile, I agree that she is short strided, especially in trot in front. She looks like her shoulders are stuck. So I emailed Amy Thalacker (vet, chiro, acupuncturist) who can look at Rosa on Wednesday when I will be teaching at her barn.
I need to shoot video of how she moves now. I am hopefully that she can be unstuck.