First Mentioned: LIAB Text 55
Clotheshorses are likely mounts. They may come equipped with fancy livery, which may provide some form of bonus in combat. This may be a form of Natural Dollamancy, perhaps allowing them to equip different kinds of livery, each with a different kind of effect.
Real World References
A Clothes Horse is a frame on which laundry is dried or, metaphorically, an individual who enjoys buying clothes and maintaining an extensive wardrobe.