I can see in the bigger pic that she's not overly upright... it's not the only factor in the trot, but it's one of them you can look for.... If you see a horse with a real straight up pastern they're gonna be choppy :~D
If she carries her head high, the trot would be rougher. They don't have to have their noses in the dirt, but you don't want them to have their heads up where to see you have to look around them:). If their head is up it hollows out their back.
I don't know if that is what she is doing, just a suggestion.
Becky