Duster (see icon,) is in between the size of an average mare and a filly. Her size would make her speed, evasiveness, and stamina a force to be reckoned with, but her defenses on the lower end.
She'd specialize in scratching and jabbing with her hooftoes, but her real power is in outrunning attacks. She's a nimble dodger from years of practice running with stampeding giant ancient herbivores and hack-and-slash tactics really wouldn't do much. Kicks or punches she'd weave around, maybe slide under the foe, grab a leg, and pull to trip them up. She's also very cunning and would not hestitate to resort to tactics that cause your own attacks to get thrown back in your face.
If you really want to bring Duster down, use magic. She comes from a primitive society where shamanistic magic is the only kind of magic not considered unspeakably evil. Standard Equestrian magic is unheard of outside of folktales used to scare children (and it's called "witchcraft") and your average unicorn with any decent attack spell can put the breaks on the speed demon eohippus.