As Opal tells us without a hint of exaggeration, everything that happened to her that summer happened because of Winn-Dixie. That includes meeting Gloria Dump for the first time, the lady who would go on to strike up a friendship with Opal.
If Winn-Dixie hadn't introduced them—insofar as a dog can introduce two people to each other—then Opal and Gloria would neither have met nor become friends.
It happened one day when Opal was out riding her bike, with Winn-Dixie in tow as always. After exchanging some unpleasantries with the bald Dewberry boys—their mom shaves their heads because one of them once got fleas from the family cat—Opal rides off to the forest, where Winn-Dixie has run on ahead.
One of the Dewberry boys, Dunlap, tells Opal that she'd better get her dog out of the forest otherwise he'll be eaten by the witch who lives there. When Opal finally catches up with Winn-Dixie, she sees a lady feeding him peanut butter. That lady is Gloria Dump, who most certainly isn't a witch. In fact, she's a very kind-looking woman.
Opal feels relaxed in the company of Gloria, and as they eat peanut butter sandwiches together, Opal opens up and tells Gloria all about her past.