That thoroughgood is really wide! I think it'd be too wide for Squiggy.
Can you measure the gullet width on a saddle that works for her?
I might have a good one for you. It's a Crosby jump saddle, 17 inch with all the fittings. It fits Mac acceptably, so might work for Squiggy. However, one lady wants to see and may buy. If she doesn't I 'll let you know.
It's a screaming deal at $400 for all, including girth and pad.