I've been thinking about what happened on Lola, and all her stumbling, and I've come to the conclusion that the poor girl probably does have a little something going on in the right hind, but I also think she is not well conditioned, and breaks down a bit more when she is tired. And right now, it's too easy for her to get tired.
I have consulted with a vet, before embarking on this problem. Lola is not obviously lame. I notice her right hind moving funny, but someone who didn't live with her and see her every day, wouldn't notice it. My vet didn't nor did my trainer. But I know it's there. But until it's more obvious, there isn't much to do about it. But I can work on her conditioning.
Yesterday, James and I embarked on a more scheduled pattern of riding, to build up the horses. We jogged (read trotted) Lola and Woody for 2 miles, splitting the time posting on either shoulder so as not to hammer one shoulder more than the other. We worked on gentle collection; I kept Woody VERY collected since he's in better shape, and James rode Lola lightly collected since she isn't in great shape. There were very few stumbles, and both horses performed well.
We then went to the round pen and worked on cantering in the correct lead. My round pen is big enough for riding, and we kept the horses on the rail to keep the circle as big as possible and avoid tight circles that could unduly stress joints. Lola was doing better at taking the correct lead, although still a little reluctant to take the right lead. James did a good job of riding her in the correct position to facilitate a proper lead departure.
We cantered in each direction for 4 circles, then rested the horses. We did this for 3 sets, or a total of 12 cantering circles in each direction. Lola was wet, but not soaked or lathered at the end of this activity. Woody was warm and a touch wet, but he looked to be in better shape than Lola.
I hope to continue this program and advance it as the horses respond. FYI: Lola's manners are much better since the frequent riding has begun. In fact, all the horses' manners are improved. Amazing what giving them a job will do to sweeten their disposition.