Ok, I have to disagree with several posters before me. This filly is not cowhocked or camped under. In fact, her legs are her best feature. Her front legs are very straight and neither too narrow not too wide. Pasterns are normal, if the tiniest bit long. Angle is good, hooves look good. She is pretty downhill, but she is still growing so might be croup high right now.
The big thing that makes her not breeding level and will affect her a bit (no Grand Prix dressage, ok?) is that her neck is really short compared to her body length, is set on low and is way under muscled. The muscling can be changed, the small/short neck cannot. Trim up her mane and it will help make her neck look longer, give her a hunter look.
I think you totally lucked out. It couldn't possibly be that her calmness is due to malnutrition? But, no, since you've had a her awhile.