Centered Riding, by Sally Swift, is another classic book with a lot of excellent visuals and imagery to help really explain how you should be physically moving and the sensations you should be aiming for. Swift had rather severe scoliosis and so developed a very keen sense of the how of things like feel and balance because she was sort of starting behind the 8-ball and didn’t have the innate sense of balance that she saw in other more “able bodied” riders. I think a lot of what she says is very useful to those of us who have to spend many hours behind a desk, or who have weakness/stiffness etc because she acknowledges the how-to of physicality.
Often, trainers - even if they are very good teachers! - can forget or simply not personally relate to the physical challenges of someone who isn’t on a horse x-hours a day. Very good riders and trainers often do have their sense of feel and balance so internalized that expressing it in terms of what us mere mortals need to do with out bodies is a real challenge. I think this can apply to trainers who are very worthwhile good teachers and not necessarily a sign to head for the hills. If you find some of the imagery suggested in this thread or in books to be helpful, I’d encourage you to share that with your trainer. It should be easy for her to incorporate those specific images, and ideally it will help her to a) understand more generally the kinds of directions that are impactful to you and b) develop suggestions/imagery of her own to help you with other challenges as you progress.
A very simple example of this, is that my coach often says “elbows” if I am getting locked up - because that is the joint that’s connecting with the bit. When I think of correcting “elbows” things do improve, but only marginally. However, if I think of shoulders and thumbs (so a more whole-arm realignment) the improvement is significant - the actual change is really seen and felt in the elbow, but but physically I need to think about the adjustment differently. I explained this to my coach, and now she says “soft in the arm.” it’s very minor, but it’s more effective for me.