She wore no coat; her blouse was covered with grass and seeds, and it was open at the neck; her hair hung loose and disheveled; one side of her face bore a stain of grass and dirt and a suspicion of blood; the other was red and white; her eyes blazed; beads of sweat stood out on her brow and wet places shone on her cheeks.

As she began to strain on the halter, pulling herself closer to the fiery pony, the outline of her slender shape stood out lithe and strong.
Bo had been defeated in her cherished and determined ambition to ride Dale's mustang, and she was furious.

The mustang did not appear to be vicious or mean.

But he was spirited, tricky, mischievous, and he had thrown her six times.

The scene of Bo's defeat was at the edge of the park, where thick moss and grass afforded soft places for her to fall.
It also afforded poor foothold for the gray mustang, obviously placing him at a disadvantage.