Mrs. Arable is Fern's mother.  She helps to raise Wilber while Fern is in school.  She gives the baby pig a noon time feeding.  She is also instrumental in suggesting that Fern sell the pig to her Uncle Homer so that Fern can still visit Wilber.  This is good because it gives Fern more time with Wilber but sad at the same time because Fern knew that Uncle Homer's family would be having Wilber for Christmas dinner.