Aside from Susan Nunsuch, Olly is the only other female member of the Egdon chorus that we hear about, mainly at the beginning of the novel. She features in the Guy Fawkes Night bonfire celebration on the heath and she dances with Timothy Fairway. She also walks Mrs. Yeobright home, or until they come across Diggory and Thomasin. Olly proves herself to be an honest and forthright woman in that scene, and she isn't afraid of speaking truthfully to Mrs. Yeobright. But she isn't a particularly savvy woman.
Olly, though without the tact to perceive when remarks were untimely, was saved by her very simplicity from rendering them offensive. Questions that would have been resented in others she could ask with impunity. (1.4.6)
Olly helps us to learn more about Mrs. Yeobright in this scene and also injects some local color and dialect.