Opal's mother left the family when Opal was only three years old. In that sense, Opal has met her mother but has no real memory of her at the time that the story is set in the novel.
In chapter 4, Opal asks her father to tell her ten facts about her mother so that she could recognize her if she ever returned. Regardless of this, her father makes it clear that Opal's mother will not be returning to the family. However, with the list, she gets to learn a little about the woman who abandoned the family. She writes the list down and recites it to Winn-Dixie. However, in spite of living every day in the hope of her mother's return, Opal and her mother are not reunited during the summer in which the story takes place, and it seems unlikely that they ever will be.