Boy, she's a pretty thing! That is just the cutest picture.
Looking at her legs, back and loins, I would say hundred pounds tops, I'd walk and trot her with that weight and see how she carries it.
Surely there's got to be a tough little kid somewhere in the Thelwell mold who would like such a pretty little girl, even if she's a bit "skeery".
An advanced Pony Clubber would be great.... but my trouble has been finding anyone skilled enough and small enough. I would free-lease her... heck, I would keep her here and help a kid take her wherever they wanted to go with her. I just don't travel in those circles.