Kylie actually, all three that I've posted here might help you and your mare. The last one in particular is the one that shares some similarities to your situation. In the second video (One-rein stop), what you want to look for is that that mare does it without being stressed and you want to work it regularly until she can do it with a relaxed attitude. Once that gets reliably good at a walk, trot and lope then you can start to work in a forward lateral bend which I'm going to cover in the next video. In the meantime, check out this horse! This is pretty similar to what I'm aspiring to.