Mrs. Prodd is one half of the husband-wife farming team that takes Lone in after Mr. Kew's beating and heals him.
While Mr. Prodd plays a bigger role in the story and is the one to work with Lone on the farm, Mrs. Prodd sings to Lone, feeds him, and bakes him a birthday cake.
The fact that she feeds him is especially significant. The memory of that kindness is what inspires Lone to allow Janie and the twins to live in the shelter, which grows the gestalt. As Lone debates whether to let him in, he recalls her feeding him:
Unbidden, an image appeared to him—Mrs. Prodd, a steaming platter of baked ham flanked by the orange gaze of perfect eggs, saying, "Now you set right down and have some breakfast." (1.25.39).
So, one of her major roles is to "prod" (get it? her name!) Lone's evolution. The other is to refrain from giving him a full sense of belonging, for she only sees him as a substitute for her fantasy son Jack.
Finally, once she gives birth to Baby rather than Jack, she dies, driving Mr. Prodd mad as he tries to find her.
And that's Mrs. Prodd for ya! Now set right down and have some breakfast!