I've increased her grain a little, since I've started her in work. Took her for a walk the other day, just went one lap around the crop field next to my property. It's a hill, so I did take her to the top of it instead of just walking around it, to work her back a little more. Today, I tried to lunge her, but I could only get her to go one direction. She seemed afraid to have me and the whip on her left side and I couldn't even get her turned away from me in that direction. So I guess I need to train her to lunge. I did do some work on yielding her shoulders away in both directions, and then did some turns on the haunches and forequarters, and some backing up, to work her muscles.
Will the work to train her to lunge properly help build her muscles? it will be yielding her shoulders away from me, yielding her hindquarters away, sidepassing, etc., but I normally train for short periods of time (10-20 minutes, until I'm bored and can end on an improvement), and I don't know if that would be enough work to build muscles.
I'm still not riding her, but I did get a saddle pad for her. It's a $150 pad that I got for $60 on amazon.com (with free shipping!). I had bought a 32x32 pad for $70 at tsc, but it was way too big. This one only has a 27.5" spine and after trying it on her, I don't think I would use anything bigger. The saddle doesn't fit her right now, I hope it's just because she's thin and doesn't have any muscles. It almost sits on her withers in the front, and the back of it doesn't touch her back.
I don't know if she's gained weight since the last update, but I haven't taken progress pictures.