[RC] great saddle hunt: narrow twist seat on wide tree - Susith
For a horse that changes shape dramatically probably the flexible panel
will work well for her. In terms of narrow twist, the Free n' Easy has a narrow
twist and comes in different widths, and you can adjust it yourself to fit you
and your horse. It does seem a little high at first, but I've gotten used to it
and it's become one of my favorite saddles.
The only other one I'm familiar with that has a narrow twist is the
Synergist, but that's a custom made saddle which might not work out well for
your mare if she's still changing shape.