She looks great. You have done an AMAZING job. Anything experienced with horse rescue would never say she should look better at this point. Many wouldn't have improved to the degree she has at her age and the neglect she appears to have come from.
TCC is a great feed. I feed it to our Arabs and rescues. She doesn't need additonal supplements, as everyone has basically mentioned. I would feel additonal alfalfa pellets or cubes with the timothy hay, and that would be it.
Her topline might not ever fill totally out if she has spent years not being used and being neglected. It is a muscle thing, not a weight thing, in her case.
Riding and lots of turn out, if possible, with lots of acerage will help build it back up.
I have an Arab mare who has always gotten top care, and due to never having been ridden, train or having a lot of turn out, her topline looks poor. We are hoping to get our fence finished here (we bought her from her breeder in July at 8 years old) and turn her out in the hills on 20 plus acres and see what happens.