What kind of feathers are on Curley's wife shoes?
Ostrich feathers. And the shoe style was someting called "mule."
Wikipedia: "Mule, a French word, is a style of shoe that is backless and often closed-toed. Mules can be any heel height - from flat to high. The style is predominantly (but not exclusively) worn by women.
From OMM, p.26....
[[Both men (George and Lennie) glanced up, for the rectangle of sunshine in the doorway was cut off. A girl was standing there looking in. She had full, rouged lips and wide-spaced eyes, heavily made up. Her fingernails were red. Her hair hung in little rolled clusters, like sausages. She wore a cotton house dress and red mules, on the insteps of which were little bouquets of red ostrich feathers. "I'm lookin' for Curley," she said. Her voice had a nasal, brittle quality.]]